ive done all of that, and the changing the low pass filter on my cd player does not help the crackling and distortion.

switch the RCA side around just to see if it makes a dif. if not id say make sure they are all tight. ive had a few dif RCAs of the same brand fail on me even when bought new. i finally bought new better brand ones and all ahas been good besides the one side comeing loose form my beat lol. pinched the fittings a lil tighter and no prob. when it was loose it did make a crackle nise when turned up too but all ended up good

make sure your rcas are plugged into your line in'* on your amp and not line outs!!