sony audio system failing, where?

I have a Sony CDX-GT72W head unit, a Sony XM-ZR1852 amp, and 1 XS-L120P5A Subwoofer. It all has been working fine for about a year, but recently, the subwoofer has been cutting out and staying off - until I restart the head unit. The subwoofer does seem to fail due to bass, but a very small amount. That is, I'm not blasting it; it dies at low levels. About 50% of the time, restarting the head unit fixes the issue, but only until the next bit of bass. I've checked all the wiring, and I think it is a hardware issue, but any idea which piece is most likely failing? Thanks! (Also, why does my head unit make ultra high-pitched sound when it is on - similar to that of an old TV?)

I would make sure the ground is nice and secure and reading a good ground contact at the amp on a volt meter. If that is crossed off the list for sure. Then the amp would be the next likely culprit. Could be a bad power/ground terminal on the amp or possibly a transistor going/or bad.

When the amp cuts out, what LEDs are lit up on the amp?