coreaudiod constantly at around 12.5% CPU on Catalina

The problem seems to be that the Audio preferences folder is missing for your user. I solved this with a variation of the solution linked to by dafal:

1. Create a new user on the Mac
2. Log in as the new user
3. Copy the folder ~/Library/Preferences/Audio somewhere where your main user can reach it – a USB stick for example. I copied it to the Public folder of my main user.
4. Log out and log back in as your main user
5. Copy the Audio folder into ~/Library/Preferences of your main user.

For me, the fans stopped running within seconds after I did this. I verified that coreaudiodwas down to 0.0% cpu. No restart was necessary.

(To access the Library folder in the Finder, hold down the shift key while you open the "Go" menu. One of the items in the menu will be "Library").