So weird. Have been having this issue with my iMac for over a year now. Even when I move my mouse it goes up and down. Switched speakers and checked wires, it is still doing it. Any thoughts?
iMac 27", macOS 10.15
Reset the SMC, as per > How to reset the System Management Controller (SMC) on your Mac - Apple Support
Then startup with an NVRAM reset, as per > Reset NVRAM or PRAM on your Mac - Apple Support
If those don't cure it > Use safe mode to isolate issues with your Mac - Apple Support
Sound issues: Volume goes up and down arbitrarily
