x2 on the grounds and on using the DMM. You can pick one up at RadioShack for $20.
If both subs are doing this I doubt it's the surround (unless you somehow beat the hell out of them and managed to damage both of them). I would not rule out the amp though, even though it's new. I have a friend who has the same problem with crackling subs (he tried two sets) and it turned out to be the amp.
Maybe try hooking the speaker wires from your amp to someone else's subs... that will tell you for sure if it's the subs or not. //content.invisioncic.com/y282845/emoticons/thumbsup.gif.3287b36ca96645a13a43aff531f37f02.gif