Quick answer: Mute or route the bus that actually feeds the output, remove unintended sends, and verify each player's bus assignment so no sound has an alternate path.
You mute your SFX bus but faint sound still comes through. A send to a reverb or another bus provides a parallel route that muting the source bus doesn't cut.
How to fix it
1. Check for sends
In the Audio panel look at the muted bus's Send target; a copy of its signal reaches output through that bus regardless of the mute.
2. Mute the right point
Mute the bus that everything ultimately flows into (often a group bus), or mute the send target too, so there's no alternate path.
3. Verify player routing
Confirm each AudioStreamPlayer's bus is the one you muted; a stray player on Master bypasses your muted SFX bus.
Catching the ones you can't reproduce
The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.
Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.
This is where a tool like Bugnet earns its place. Its SDK captures every Godot error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.
Ship the fix, watch the signature disappear from the next build. That's how you know it's really gone.