arc amp switches?

my 2100cxl is on the fritz, one of the channels  gives off a horrible scratching sound like if a speaker had been blown.  I found it was the channel and when I emailed arc audio about it i got this response,

I 've heard gain knobs making noise through the speakers (scratchy sounds) while they are being adjusted. However wd-40 ain't gonna do much. If i were you, I 'd just send it in before any thing else happens. That's a nice amp you have.

Thanks for the replies.  Yesterday I started checking out the setup and when I was changing a few things my OTHER arc amp started doing the same thing.  I set it up to replace the one I had and now I think it may be the electronic crossover I have in between everything.  The ground on it wasn't on very good for some reason so I pulled it off and listened and the scratchy ugly sound was bad.  when I recconected it, it was only on the right side again.  I switched the rca's to see if it was one of them, but I'm pretty sure it's the xover.  It's pretty dusty too, (i live in the desert) so I'll try the contact cleaner thing.  Thanks again.