I'm having a somewhat unusual problem. If I have my stereo up to a good listening volume, and slow down the car, the speakers are intermittent for a few seconds. It seems to go away once I speed up again. So far I haven't done the Big 3 but I put in one of them (Battery > Frame ground wire, 4 GA). Here's my audio set-up:

2x 150W RMS Amp for subs
4x 60W RMS Amp for speakers

It used to also cut out when I would turn the engine off, but now that I put in the big fat ground wire, that doesn't seem to happen anymore. Should I go for the nex "Big" and wire a ground from the block / alt, or could this be the battery? (Battery is a 5-year Delco that came with the car, and the car is now 5 years old)

Maybe something different altogether? I was thinking if it's not the main grounds than maybe the ground to the HU? Still have to work out what seems to be a ground look (hissing if I turn the amp gains up more than ~25% so i'm running them very low)

Forgot to mention -- seems to happen more often if I am braking or turning hard.

Def Sounds like a loose connection somewhere to me.

im 90% sure its just a loose wire. That would explain why it cuts on turns.

its most likely your RCA wires, Are they cheap one?

Looks like loose wire was the answer. The battery terminal was loose. The one I have is like a regular battery terminal, with a smaller terminal on top. The main terminal was tight so the rest of the car worked fine but the "sub-terminal" was a little loose and there was some dirt that got between the terminal and the ring on the end of the wire. I cleaned them both and made it nice and tight with a wrench and it's no longer cutting out.

As far as the RCA's go, i have Radio Shack RCA's on the subs and Scosche RCA's on the speakers. I have some noise on the line but i'm fairly certain it's a ground loop (I know the wiring harness on the HU is a little loose -- haven't had time to take apart the dash and fix it, as well as run another ground wire)