Audio Systems: speaker problem, high pitch, ground loop

Question
for a while now I have a high pitch whinning noise coming from my 6x9's fosgate punches. I'm not entirely sure what causes it. My amp that I'm using is a 460w Duel. People that I talked to about said that I might need a filter or the ground is making that happen. So I just want to hear it from a professional. Please tell me thanks

Answer
yes there is something called a ground loop which will cause different problems,  usually its a whiney engine sound that actually changes pitch when you rev the engine.  It usually is developed between your cd player and amplifier. the easiest way to test this is to simply disconnect the RCA lines at the amplifier and see if the noise goes away.  if so, you can get a ground loop isoloator at radioshack and put that on the RCAs.  If not let me know. These can be very difficult to get rid of without the isolator.
Good luck and please let me know how it goes.