I tried adding a second capacitor in parallel and even a 3rd. It actually makes the problem worse.

For the volume control I'm using a 22K potentiometer with the wiper connected to Vi in the schematic, one side connected to ground and the other side connected to my PIC. Initially this did cause clipping around half way so I added an extra 22K resistor between the PIC and the pot. Now the max volume is just under where it starts to clip.

As a test I removed the ground from the left side of the pot. With the TDA2030 that would have caused a lot of noise through the speaker but on the TDA2050 it was fine until I ran the code in the PIC and that same resistor exploded violently.

As I have it now the resistor is fine until I turn the volume right up. Since this is about the limit of the chip's power before clipping and you recommend a 0.6W resistor then I think it's simply that my resistor can't cope rather than any destructive high frequencies. I will still check for those anyway just to be on the safe side but I think a tougher resistor should solve the problem.

Will a 0.6W resistor be suitable for running a 4Ohm speaker too?