So I had a crazy problem with the audio output on Big Sur. Distorted laggy… unusable.
I was able to solve it with the following:
Open the App ‘Audio MIDI Setup’. This is where the real audio configuration is done on the Mac.
Look for an Aggregate-Audio-Device listing.
I removed a USB ‘Mic’ that was listed as an output. The problem disappeared. My problem was caused by the fact that my Elgato Wave:3 (a virtual mixer) was also in this list causing the crazy lag and loop on the output channel.
My current list has two items, a pair of bluetooth headphones and my external headphones jack.
Hope this might help others in this situation.