Make sure you have a really good ground...

If your interior speakers haven't been amped before, then it's possible you didn't have a good ground...

Your sub generally won't put out that kind of high frequency noise, so you don't notice it... Unless you've got really bad interference, the most you'll get out of your sub, usually, is a popping noise when you turn things on and off...


Currently, I've got my 4 channel grounded to the same place as my sub amp... Well, specifically, TO the ground port on my sub amp... lol

I know it's not the best thing to do, but it works great, and no interference! (Except for when I pinched the ground wire in one of the seat brackets...)