You know what i don't ever post on here, But since it sounds like ya need the help , and since no one is asking these Questions , here it goes.
What amp is it?
What sub(s) and Speakers are they?
What Bat do u have up front?
What Alt are you running? what size amps is it?
How did you set the Gains on the amp?
and the last one , What size Power/ground wire?
And to answer your question just from the info i have seen, it does sound like something hooked up to the amp is loose , or a Bad/dirty fuse or the amp could be going out/dieing/dead, oh and from what i heard your bats dead? that could be the reason your amp waz cutting out(Because of the Voltage Drop)