bass cutting in and out?

[Captain McFunk]

Hey guys, I've got a Type R 12" subwoofer and an M500 amplifier in my Camaro. I've got a LOC from the factory amp to the aftermarket amp to pull the signal. it's worked fine and sounded great up until about a month ago. The problem i'm having is this:

When i start the car, there is no bass. this is when the volume level is between 0-5. The only time bass comes on is when I turn the volume up to 15-20, then the bass kicks in all at once. If you turn it back down, the bass stays for about 15 seconds, and then cuts out again. The amp has power the whole time.

I've never ran into this issue before, and i've had stereos in my last 4 cars installed by myself.

Anyone have any thoughts as to why the bass would "activate" in accordance with the volume level?

Thanks!

Adam