Sub making weird hum?

I have a Clarion DXZ535 HU, with a PG Octane 5.0.1 amp going into a JL 2x 10w0 factory cabinet.  Every once in a while, I get  a loud intermittent humming noise from the subs that sounds like a RCA has been unplugged, or a bad ground.  I have double checked all my connections, and all my wiring, and everything looks as it should.  I'm pretty sure it's not from the HU, since I turn the sub level all the way down, and it doesn't get any quieter.  It's not from cell phones, or any of my neons or radar detector, as I've tested all those theories.  The setup has been working fine since it was installed last year until a few months ago.  Anyone have any ideas?

I'd go back to your installer.  Sounds like something's shorting out.  I imagine it's going to involve a lot of trial & error to find it - replace components until you narrow it down.

Something has changed at the same time the trouble started.  If you or anyone else didn't make the change, then the change came about by some other means:  a wire is bad that can't be seen;  a ground connection has lost connectivity due to corrosion;  etc.  You're on the right track in your thinking, and you'll have to test each wire piece by piece.  Keep notes and don't forget to unhook battery power before removing any wires.Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.