My late 2020 M1 MacBook Air has picked up a new quirk: audio from both the left and right channel is only coming out of the left side speaker. What’s odd about it is that if I play a “stereo test” video, or if I play white noise and slide the Sound Settings balance slider between left and right, then the timbre of the sound changes slightly (but it keeps coming out of the left speaker).

(What I would expect to happen with a failed right speaker is no sound from the right channel, not “right channel comes out the left side”!)

The two main ways I’ve been testing it are

• play music or white noise, slide balance slider back and forth in Sound Settings
• use the “test” buttons on each channel in Audio MIDI Setup

I’ve used an (imprecise) decibel meter app on my iPhone to make sure that I am not hallucinating. Sound pressure is highest on the left side and falls off consistently as I move away from there, including over the right side speaker. With stereo white noise, there’s a ~15dB difference between directly over the left side of my laptop and the right side.

Things I have tried that did not fix it:

• removing all third-party audio drivers (Zoom, Krisp, etc)
• upgrading from Monterey to Ventura
• booting into safe mode to test (but there’s no audio in safe mode!)
• creating a new user and testing audio
• double-checking Accessibility settings, in case I flubbed something when setting up accessibility settings for my Airpods

I haven’t popped the back off yet, although honestly other than checking connectors I’m not sure what I’ll do when I do pop it open, because I can’t come up with any explanation for both channels coming out of the left speaker, or about the timbre change. I’ve got all the tiny screwdrivers and spudgers I’d need, though, and I’m comfortable poking around a little.

I’ve had a hard time putting my finger on what exactly the timbre change is. White noise played through the right channel (still coming out the left side!) feels more distant, which might be that it’s just a little quieter, or it might be that it’s got less low end, I can’t quite tell. But it’s definitely different, and panning that white noise from left to right is a linear change, there’s no “sweet spot” at centre or anything so I don’t think it’s a phase issue or something weird like that.

Unfortunately I don’t know when it began. I think it was recent, because when I noticed it, it was not subtle. Headphones, both wired and Bluetooth, work fine. I did recently buy and connect a pair of Airpods Pro (2nd gen) but I can’t imagine how that would impact anything.

It is no longer under warranty or AppleCare.

Anybody have any idea what might be going on, or what I should try, either when I open it up or in software?