I have a 97 lexus sc with a pioneer prs x 320 amp and a subwoofer. I bought the car about 3 months ago and the sub was working great. About a month ago is stopped working. Every so often, usually when the car has been parked in the sun, the sub works, but then quits again after a few seconds. The other speakers always work fine. Any idea what the problem is? I don't think the amp is original. The car came with the Nakamichi sound system. I think someone switched the amp out before I bought the car.