Audio Amp SHIM interference

Recently added an Audio Amp SHIM to a pi zero 2 W.

Got it working connected as a snapcast client and it sounded fine.
But now I’m getting interference on the speaker output. It sounds like beating over the output.
Very similar to the noises I got on a different amplifier before I put any isolation in.

Have I blown something up?
Is this a limitation of the board?
Is there some control software which could solve this.

Thanks in advance for any help

Seems to be working OK now.
I think it was a poor connection on one of the pins.