diff --git a/js/app.js b/js/app.js
index 9215868..3fd33d9 100644
--- a/js/app.js
+++ b/js/app.js
@@ -301,6 +301,10 @@ document.addEventListener('DOMContentLoaded', () => {
     if (presetId === 'bio-vorlon') expandedAudio.startVorlonSong(); // #26
     if (presetId === 'bio-wraith') expandedAudio.startHullRegen(); // #28
     if (presetId === 'deep-event-horizon' || presetId === 'deep-icarus-ii') expandedAudio.startHullStrainMoans(); // #30
+    // Phase 3 (audio_gaps.md #46-#54)
+    if (presetId === 'sta-babylon-5') expandedAudio.startZocaloChatter(); // #46
+    if (presetId === 'ind-nostromo') expandedAudio.startTeletypeChatter(); // #51
+    if (presetId === 'ret-jupiter-2') expandedAudio.startHeterodyneDrone(); // #54
     if (presetId === 'deep-icarus-ii') expandedAudio.startIcarusBeacon(); // #31
     if (presetId === 'deep-event-horizon' || presetId === 'deep-nightflyer') expandedAudio.startVoidWhispers(); // #32
     if (presetId === 'com-protector') expandedAudio.startBerylliumThrum(); // #33
@@ -935,6 +939,14 @@ document.addEventListener('DOMContentLoaded', () => {
       case 'btn-teletype':
         expandedAudio.synthesizeTeletypeChatterPhrase();
         break;
+      case 'btn-zocalo-chatter':
+        if (expandedAudio.zocaloChatterActive) expandedAudio.stopZocaloChatter();
+        else expandedAudio.startZocaloChatter();
+        break;
+      case 'btn-hetero-drone':
+        if (expandedAudio.heterodyneDroneActive) expandedAudio.stopHeterodyneDrone();
+        else expandedAudio.startHeterodyneDrone();
+        break;
 
       default:
         telemetry.synthesizeLCARSSingleChirp();
diff --git a/js/audio.js b/js/audio.js
index df09d51..d39ee79 100644
--- a/js/audio.js
+++ b/js/audio.js
@@ -5719,9 +5719,211 @@ class ExpandedSciFiAudioSynth {
     }
   }
 
+  /**
+   * Ambient Loop: Continuous Nostromo terminal teletype chatter (#51)
+   * Dense overlapping "typed line" phrases at a 0.9-2.0 s cadence keep the
+   * effect continuous while the preset runs. Dies with the loop registry.
+   */
+  startTeletypeChatter(minIntervalMs = 900, maxIntervalMs = 2000) {
+    this._scheduleLoop('teletypeChatter', minIntervalMs, maxIntervalMs, () => {
+      this.synthesizeTeletypeChatterPhrase();
+    });
+  }
+
+  /**
+   * Continuous Heterodyne / Theremin Navigational Drone (audio_gaps.md #54)
+   * A persistent room-tone element for the Jupiter 2 astrogator deck: two
+   * detuned sines (~1040 Hz / ~1048 Hz) beating to ~8 Hz, each with a very
+   * slow independent wander LFO so the beat drifts like a vacuum-tube theremin.
+   * True node-graph bed - long 3 s attack, room-tone level, gentle 1.8 s
+   * release on stop. Re-start always fades the previous bed out first.
+   */
+  startHeterodyneDrone() {
+    this.init();
+    const ctx = this.am.ctx;
+    if (!ctx || !this.gainNode) return;
+
+    this.stopHeterodyneDrone();
+
+    const now = ctx.currentTime;
+    const level = 0.06;
+    const masterGain = ctx.createGain();
+    masterGain.gain.setValueAtTime(0.0001, now);
+    masterGain.gain.linearRampToValueAtTime(level, now + 3.0);
+    masterGain.connect(this.gainNode);
+
+    const sources = [];
+    [1040, 1048].forEach((baseFreq, idx) => {
+      const osc = ctx.createOscillator();
+      osc.type = 'sine';
+      osc.frequency.setValueAtTime(baseFreq, now);
+      // Slow independent drift (0.04-0.09 Hz) keeps the beat wandering
+      const wander = ctx.createOscillator();
+      wander.type = 'sine';
+      wander.frequency.setValueAtTime(idx === 0 ? 0.04 + Math.random() * 0.02 : 0.07 + Math.random() * 0.02, now);
+      const wanderDepth = ctx.createGain();
+      wanderDepth.gain.setValueAtTime(idx === 0 ? 4 : 3, now);
+      wander.connect(wanderDepth);
+      wanderDepth.connect(osc.frequency);
+
+      const voiceGain = ctx.createGain();
+      voiceGain.gain.setValueAtTime(0.5, now);
+      osc.connect(voiceGain);
+      voiceGain.connect(masterGain);
+      osc.start(now);
+      wander.start(now);
+      sources.push(osc, wander);
+    });
+
+    this.heterodyneDroneActive = true;
+    this.heterodyneDroneGain = masterGain;
+    this.heterodyneDroneSources = sources;
+  }
+
+  stopHeterodyneDrone() {
+    this.heterodyneDroneActive = false;
+    const gain = this.heterodyneDroneGain;
+    if (!gain) return;
+    const ctx = this.am.ctx;
+    if (ctx) {
+      const now = ctx.currentTime;
+      // linearRamp continues from the computed value, so a mid-attack stop
+      // glides down smoothly without a click
+      gain.gain.linearRampToValueAtTime(0.0001, now + 1.8);
+      (this.heterodyneDroneSources || []).forEach((src) => {
+        try { src.stop(now + 2.0); } catch (e) { /* already stopped */ }
+      });
+    }
+    this.heterodyneDroneGain = null;
+    this.heterodyneDroneSources = null;
+  }
+
+  /**
+   * Zocalo Commerce-Plaza Chatter Bed (audio_gaps.md #46)
+   * A persistent crowd-murmur bed for Babylon 5: looped pink noise through
+   * four parallel formant bandpasses (300 Hz - 3 kHz) whose centers drift at
+   * 0.03-0.11 Hz, plus an accent layer of vowelish murmur blips scheduled on
+   * the loop registry. Re-start fades any previous bed out first.
+   */
+  startZocaloChatter() {
+    this.init();
+    const ctx = this.am.ctx;
+    if (!ctx || !this.gainNode) return;
+
+    this.stopZocaloChatter();
+
+    const now = ctx.currentTime;
+    const bedBuf = this.am.createNoiseBuffer('pink', 8);
+    const bed = ctx.createBufferSource();
+    bed.buffer = bedBuf;
+    bed.loop = true;
+
+    const masterGain = ctx.createGain();
+    masterGain.gain.setValueAtTime(0.0001, now);
+    masterGain.gain.linearRampToValueAtTime(0.16, now + 2.5);
+    masterGain.connect(this.gainNode);
+
+    // Formant filter bank with slow independent center drift
+    const sources = [];
+    const formants = [
+      { center: 330, q: 6, weight: 0.3, driftHz: 55, driftRate: 0.03 + Math.random() * 0.02 },
+      { center: 760, q: 5, weight: 0.24, driftHz: 130, driftRate: 0.05 + Math.random() * 0.03 },
+      { center: 1500, q: 4, weight: 0.16, driftHz: 260, driftRate: 0.07 + Math.random() * 0.03 },
+      { center: 2600, q: 3, weight: 0.08, driftHz: 480, driftRate: 0.09 + Math.random() * 0.02 }
+    ];
+    formants.forEach((f) => {
+      const bp = ctx.createBiquadFilter();
+      bp.type = 'bandpass';
+      bp.frequency.setValueAtTime(f.center, now);
+      bp.Q.setValueAtTime(f.q, now);
+      const drift = ctx.createOscillator();
+      drift.type = 'sine';
+      drift.frequency.setValueAtTime(f.driftRate, now);
+      const driftDepth = ctx.createGain();
+      driftDepth.gain.setValueAtTime(f.driftHz, now);
+      drift.connect(driftDepth);
+      driftDepth.connect(bp.frequency);
+      const bandGain = ctx.createGain();
+      bandGain.gain.setValueAtTime(f.weight, now);
+      bed.connect(bp);
+      bp.connect(bandGain);
+      bandGain.connect(masterGain);
+      drift.start(now);
+      sources.push(drift);
+    });
+
+    bed.start(now);
+    sources.push(bed);
+
+    // Crowd accents: murmur blips layered over the wash
+    this._scheduleLoop('zocaloAccents', 2400, 6800, () => {
+      this.synthesizeZocaloAccent_();
+    });
+
+    this.zocaloChatterActive = true;
+    this.zocaloChatterGain = masterGain;
+    this.zocaloChatterSources = sources;
+  }
+
+  stopZocaloChatter() {
+    this.zocaloChatterActive = false;
+    this._stopLoop('zocaloAccents');
+    const gain = this.zocaloChatterGain;
+    if (!gain) return;
+    const ctx = this.am.ctx;
+    if (ctx) {
+      const now = ctx.currentTime;
+      gain.gain.linearRampToValueAtTime(0.0001, now + 2.0);
+      (this.zocaloChatterSources || []).forEach((src) => {
+        try { src.stop(now + 2.2); } catch (e) { /* already stopped */ }
+      });
+    }
+    this.zocaloChatterGain = null;
+    this.zocaloChatterSources = null;
+  }
+
+  /**
+   * One crowd "voice" blip for the zocalo bed: a short formant-filtered noise
+   * impulse with a slight pitch glide, sometimes doubled. Self-releasing.
+   */
+  synthesizeZocaloAccent_() {
+    const ctx = this.am.ctx;
+    if (!ctx || !this.gainNode) return;
+
+    const now = ctx.currentTime;
+    const count = Math.random() < 0.3 ? 2 : 1;
+    let cursor = 0;
+    for (let i = 0; i < count; i++) {
+      const t = now + cursor;
+      const center = 380 + Math.random() * 1500;
+      const glide = Math.random() < 0.4 ? (40 + Math.random() * 90) : -(30 + Math.random() * 60);
+      const dur = 0.1 + Math.random() * 0.15;
+      const buf = this.am.createNoiseBuffer('pink', dur + 0.1);
+      const noise = ctx.createBufferSource();
+      noise.buffer = buf;
+      const bp = ctx.createBiquadFilter();
+      bp.type = 'bandpass';
+      bp.frequency.setValueAtTime(center, t);
+      bp.frequency.linearRampToValueAtTime(Math.max(200, center + glide), t + dur);
+      bp.Q.setValueAtTime(2.2 + Math.random() * 1.5, t);
+      const env = ctx.createGain();
+      env.gain.setValueAtTime(0.001, t);
+      env.gain.linearRampToValueAtTime(0.05 + Math.random() * 0.04, t + 0.03);
+      env.gain.exponentialRampToValueAtTime(0.001, t + dur);
+      noise.connect(bp);
+      bp.connect(env);
+      env.connect(this.gainNode);
+      noise.start(t);
+      noise.stop(t + dur + 0.05);
+      cursor += 0.09 + Math.random() * 0.15;
+    }
+  }
+
   stopAllLoops() {
     this.stopMedicalMonitor();
     this.stopStationSparks();
+    this.stopZocaloChatter();
+    this.stopHeterodyneDrone();
     Object.keys(this.loopTimers).forEach((key) => {
       this._stopLoop(key);
     });
diff --git a/js/config.js b/js/config.js
index 26aa46a..bb08186 100644
--- a/js/config.js
+++ b/js/config.js
@@ -510,7 +510,8 @@ const UniverseRegistry = {
       { id: 'btn-chirp-single', label: 'ASTROGATOR BEAT' },
       { id: 'btn-chirp-sweep',  label: 'ANALOG GLISSANDO' },
       { id: 'btn-relay-click',  label: 'TAPE REEL SPOOL' },
-      { id: 'btn-tape-spooler', label: 'DUAL-REEL TAPE SPOOLER' }
+      { id: 'btn-tape-spooler', label: 'DUAL-REEL TAPE SPOOLER' },
+      { id: 'btn-hetero-drone', label: 'HETERO-DRONE TONE' }
     ],
     presets: {
       'ret-jupiter-2': {
@@ -903,6 +904,7 @@ const UniverseRegistry = {
       { id: 'btn-commlock',    label: 'COMMLOCK CALLING TONE' },
       { id: 'btn-sevas-spark', label: 'CONDUIT SPARK ARC' },
       { id: 'btn-station-ecg', label: 'CLINICAL VITAL (ECG)' },
+      { id: 'btn-zocalo-chatter', label: 'ZOCALO PLAZA CHATTER' },
       { id: 'btn-belter-telemetry', label: 'BELTER JURY-RIG TELEMETRY', span: 2 }
     ],
     presets: {