PWM and audio noise

[kenif]

What everyone else says, plus:
Declare a ground star point and make all grounds radiate from that point - no daisy chains.
You should be able to trace ground noise origin with a scope.
Electrolytic caps are the bastard love child of a car battery and an RF antenna, replace with tant or ceramic if you can.
Also, make sure all caps are low ESR/ESL like TY.

[keithv]

Thanks for all the suggestions. I've been sidetracked by another project, but I will revisit this and give them a try and let you know how it works out.