I swear I got the one with the hex on it.

Dunno, all that stuff sounds like "par for the course" in most D-I-Y car stereo installations. In fact, I've gotten to the point where I consider it a bad omen if I don't injure myself in the process somehow.

I mean, it's always something. Either you don't have the right plug or part for something and you need to rush to Radio Shack with your car half-dismantled, or you slip and give yourself a nasty cut while trying to pry off an interior panel, or you burn yourself with the soldering iron (don't feel bad, I still do that with alarming regularity and I've been doing it for years).

Can I get an amen, people?

And it sounds like the noise thing might in fact be a faulty amplifier, so you can't blame that on a curse. However, I would triple-check all wiring running to the amp, especially power wiring and fuses, just in case.

And what were you doing wearing a diamond bracelet while installing a stereo?

And it happens as soon as the head unit is turned on, with both the sony and the empeg.

Hmmm... you didn't mention a second head unit at first. How are the power and amplifier signal wires connected in this two-stereo arrangement?