I'm told that there are inline RCA filters, but I'll guess this is a poor methode of masking the problem. any comments?

These filters are supposed to break the ground loop between the amp and the head unit, if that's what you've got. However, they tend to reduce the frequency response of the sound traveling through them. The ones at Radio Shack are reported to have bad frequency response specs, and there is supposedly a different kind which have OK specs, I don't remember whether the part number of the "good" one ever got repeated to me and put in the FAQ...

One of the noise-troubleshooting documents linked from the FAQ has an interesting perspective: These filters cost money. Whereas locating and fixing your ground loop problem (assuming it is a ground loop) is free. The filters would just be an expensive band-aid on an existing problem that would never get solved.