I'm still having this issue outlined in this old thread:
Long story short, I have constant speaker whine through my 6x9'* and occasionally my subwoofer amp does not work.
For the whine: I've tried ground loop isolators to no avail. My power wire is no where near my RCA'* (which are only a foot or two long because I used the stock headunit, thus wiring back to the trunk). I've redone, checked etc my grounds. I've disconnected the cap, which actually made the whine a little louder and the bass loss more frequent.
For the bass: Just yesterday after a 45 minute bass-less drive, I thumped on the amp with my hand and it kicked on. The "Protect" light was not on before I hit it.
Any ideas about either?