I've got the mmc690's in the rear of my car right now, and i'm getting some hum from the rears only. it's odd, because i'm running those AND a pair of the mmc6500's in the front, off the same amp (c400) I don't get the noise out of the fronts. nor the sub. I am going through a ground loop isolator on the rears, which seems to dull it down a bit, but it's still there. My grounds are ok, and everything looks in order, i just can't track the source down! Anyone have any other ideas?