diff --git a/packages/core/src/runtime/init.test.ts b/packages/core/src/runtime/init.test.ts
index 8a9effa13..bde05de3d 100644
--- a/packages/core/src/runtime/init.test.ts
+++ b/packages/core/src/runtime/init.test.ts
@@ -1453,6 +1453,52 @@ describe("initSandboxRuntimeModular", () => {
     expect(decodeSpy).toHaveBeenCalledTimes(2);
   });
 
+  // Scheduling does NOT replace the active set: it bumps a generation, which
+  // only rejects schedules still in flight. Every source already started keeps
+  // playing and there is no per-element dedup, so rescheduling on its own laid
+  // a second buffer source over every sounding clip — the whole mix doubled,
+  // slightly out of phase, from one mute click until the next pause.
+  it("stops the running sources before rescheduling on a data-hidden toggle", () => {
+    const root = document.createElement("div");
+    root.setAttribute("data-composition-id", "main");
+    root.setAttribute("data-root", "true");
+    root.setAttribute("data-start", "0");
+    root.setAttribute("data-duration", "10");
+    root.setAttribute("data-width", "1920");
+    root.setAttribute("data-height", "1080");
+    document.body.appendChild(root);
+
+    const audio = document.createElement("audio");
+    audio.setAttribute("data-start", "0");
+    audio.setAttribute("data-duration", "10");
+    audio.setAttribute("data-hidden", "");
+    audio.load = () => {};
+    audio.play = vi.fn(() => Promise.resolve());
+    root.appendChild(audio);
+
+    window.__timelines = { main: createMockTimeline(10) };
+    initSandboxRuntimeModular();
+    const player = window.__player;
+    player?.play();
+
+    vi.spyOn(WebAudioTransport.prototype, "decodeAudioElement").mockResolvedValue(null);
+    const stopSpy = vi.spyOn(WebAudioTransport.prototype, "stopAll");
+    const generationSpy = vi.spyOn(WebAudioTransport.prototype, "startGeneration");
+
+    audio.removeAttribute("data-hidden");
+    player?.seek(1, { keepPlaying: true });
+
+    expect(generationSpy).toHaveBeenCalledTimes(1);
+    // Two: `seek` clears the graph on its way in, and the toggle's own
+    // reschedule clears it again. Only the second one is what this covers —
+    // without it the count is 1 and the reschedule stacks on live sources.
+    expect(stopSpy.mock.calls.length).toBeGreaterThanOrEqual(2);
+    // Order matters, not just presence: stopping AFTER the reschedule would
+    // silence the clips it had just started.
+    const lastStop = Math.max(...stopSpy.mock.invocationCallOrder);
+    expect(lastStop).toBeLessThan(generationSpy.mock.invocationCallOrder[0] ?? 0);
+  });
+
   it("does not stamp Studio timing on GSAP targets inside authored timed clips", () => {
     withStudioIframe(() => {
       const root = document.createElement("div");
diff --git a/packages/core/src/runtime/init.ts b/packages/core/src/runtime/init.ts
index 0d184a46a..85b0c97b4 100644
--- a/packages/core/src/runtime/init.ts
+++ b/packages/core/src/runtime/init.ts
@@ -1961,7 +1961,16 @@ export function initSandboxRuntimeModular(): void {
   // A data-hidden toggle on (or affecting) an audio element must re-schedule
   // WebAudio playback so the hidden clip's source is dropped/restored mid-
   // playback. Batched to one call per syncTimedElementVisibility pass, not
-  // one per toggled node (schedulePlayback replaces the whole active set).
+  // one per toggled node.
+  //
+  // The reschedule is paired with `stopAll()` below, for the reason
+  // `setCanaries` and `applyWebAudioRate` already spell out: scheduling does
+  // NOT replace the active set. It bumps a generation, which only rejects
+  // stale schedules still in flight — every source already started keeps
+  // playing, and there is no per-element dedup. This comment used to claim the
+  // opposite and the call site trusted it, so muting a track mid-playback
+  // started a second buffer source for every in-window clip on top of the ones
+  // still sounding: the whole mix audibly doubled, slightly out of phase.
   let hiddenAudioDirty = false;
   const nodeAffectsAudio = (node: HTMLElement): boolean =>
     node.matches("audio[data-start]") || node.querySelector("audio[data-start]") !== null;
@@ -2042,6 +2051,7 @@ export function initSandboxRuntimeModular(): void {
       }
     }
     if (hiddenAudioDirty && clock.isPlaying()) {
+      webAudio.stopAll();
       scheduleWebAudioForActiveClips();
     }
     hiddenAudioDirty = false;