GarageBand for Mac: Mic audio cuts out on vocal track - but works fine in Logic Pro, Voice Memos, etc.

Symptom: When using GarageBand since early Sept. 2024, talking or singing into the mic (whether built-in or an external XLR > USB3 audio interface > MacBook Pro), the audio fades out and back in on a track.

It's almost as if there was a sort of "random noise gate" applied. (It seems to happen at higher pitches, but not exclusively.)

• Happens over playback and when recording.
• I've added nothing new to GB in a long time (nor other system plug-ins or apps).
• Tracks can have NO effects or plug-ins, including Master track, for this to occur.
• Happens in existing and new song files. 
• Occurs even with...
  • No peripherals or cables connected to the MBP, 
  • All other apps closed, and 
  • Bluetooth off (Activity Monitor doesn't yield clues, either). 
• Occurs in new GB projects, even with Audio Units disabled.
• Repeatedly rebooted, checked for updates, etc. Nothing's helped.
• SSD has > 500GB free.

Here's the thing...

When I tested this in Logic Pro with built-in mic and the XLR, the issue doesn't occur. (I use GB over Logic Pro for simple stuff, and I have a lot there that I'd rather not import into Logic Pro and tweak.)

I also tested this in Voice Memos and it worked fine. 

But upon relaunching GB, the issue returned. (I use GB over Logic Pro for simple stuff, and I have a lot there that I'd rather not import into Logic Pro and tweak.)

Having isolated this to GarageBand (again, with all peripherals unplugged and using on the built-in mic), I'm at a loss as to what's causing this (and not in other mic-ready apps).

This only started happening since around the first or second week of September 2024. I think there was a Sonoma security update that happened in there somewhere, but I can't recall.

Suggestions?

Thanks.

MacOS Sonoma 16.4.1

MacBook Pro M2 w/40GB Ram, 2TB SSD (500GB+ free).