volume fluctuations

Hey my friend has a Fosgate T1D215 in a 2002 mitsibishi eclipse. He recently bought a jl audio gmax 1200 amplifier and wired it to a 4 ohm load.  The problem is that after riding for a few minutes the volume will slowly decrease. Then after a few more minutes the volume will go back up. Its a fairly drastic change in volume. He has a power acoutik radio, its a PTID-8940NRBT which he bought with the amp. The voltage does not drop and the radio doesnt get quiet just the sub. We checked the rcas and nothing is wrong with them. The whole wire kit was a rockford fosgate 4ga kit with signal cable.

Any help would be appreciated. 

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Enjoy Life theres plenty of time to be dead

So the other speakers keep the same volume when the sub/s get quite?

If so it would have to be something from the head unit to the line getting the signal to the amp. I would try a new set of RCA's. There may be a bit that is cut or broke inside the casing. It may look fine and be hard to get or find the bad spot. While driving there are lots of vibrations that could do this to the wire. If that is completely ruled out. I would look at the RCA out on the deck and amp next. There may be a bad solder joint to the RCA connection on the head unit or amp its self.

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