This sounds like either the PWM is leaking into the signal path or the power supply is noisy. First of all, try to switch power supplies to a liner type (instead of switch-mode)…make sure it’s rated for at least 100mA. See if this helps.
If the PWM is leaking into the signal path, this can usually be helped by adjusting the high and low trim pots down in volume. Also play around with the gain trim pot to adjust the ratio of high/low trim pot volume to gain trim pot volume. This noise should decrease as you get the trim pots set in a good ratio.
Good luck.
-Brach