JL Slash Amp 500/1 makes Popping Sound when Turned on and low rumble when turned Off

Black probe on ground, red probe on the RCA shield.

At this point, I wouldn't assume anything.

There is a component that (very rarely) fails in the older 500 (may be int he V2 as well) but it's not as easy to replace as it is to make a few tests.
Hey Perry, just wondering what that component is that fails very rarely? I know this is an old thread but I've got basically the same thing except the popping only happens when power is removed (doesn't do it when I use the remote to turn it off only when power is completely removed) I've searched everywhere. Anyway, thanks for any help