Wow that would be great a picture LOL I really am in the dark on all this stuff.
I really do think I am getting a lot of noise spikes from the PC psu to.
I will follow the diagram you draw later and see if it makes it any better then I will move on to trying to filter the 12v noise spikes if there is any.
I hope so. I think your problem is more likely to be a wrong input connection than psu noise. Try it and see, then we'll think about the psu filtering later, if necessary.
To design a psu filter we'd need to know the current requirements of your amplifier. Do you know how many Amps it draws at full power, or its stated VA rating (not the 'music power')?
Judging from the size of the components I would guess (and it's only a guess) that the amp power is no more than 10W RMS (other members may have different views!). So the supply current may be ~1A.
You could try the attached. It's not guaranteed to cure the problem but should suppress at least some of the higher frequency components of any PSU interference. But before building this filter try powering the amp from a 12V battery (e.g. car battery) or other known noise-free 12V source.