subs sounds like shorting and make nois

I have a hifonics BXI 2608 2600 super D-Class Mono Amp and two 15 Kicker CVR's in a 6cubed box. The are DVC speakers, and I have them wired in series/parallel to equal a 4ohm load.  I am running two batteries (the 2 in the trunk is a tractor trailor batt). I origanally had an alpine HU installed and everything was playing great. I changed my HU to a Dual xdvd700 Head unit. When I installed this unit and proceeded to listen to music I noticed that my subs started to short out as I turned up the volume. The Dual HU only has one subwofer prong pre-out, so I bought a spliter and installed it, still did the same thing. I changed the Audio cables and they are not running parallel with batt wire. I also noticed that when it started to sound like its shorting out, it seemed the subs were pulsing slightly and have like a flat knocking sound. I turned all the controls on the amp down and HU (bass and subwofer wise),  and it played fine but  with a lil bass it does the whole shorting out thing. As it was doin this I unplugged the new audio cables, where I was to hear a whining (hissing) noise. I had turned the car off at this point and it had that noise through the subs with no audio cables. The amp does not seem to flicker or anything as this is goin on.

Any help to what my problem is would be greatly appreciated. Thank You!

Remove the bottom cover of the amp.  Notice very near the Power and ground input terminals.  There are a boatload of capacitors there.  Is the vinyl coating on the caps yellow in color?   If they are yellow, I am pretty sure that they are defective.  It will be a costly repair, mainly because of all of the blingification that has to be removed to get to the board.

If someone you know has a stiffening capacitor that you can borrow, install it as close to that amp as possible.  This may fix your problem without having to pay 150 dollars or so to get it repaired.