Mk 4 loud hum and where I found the problem..

This is just a FYI for someone who may come across this same thing. I had a loose RCA input that wasn't making ground (I use the nylon spacers on the new gold RCA). At any rate I guess the grounding ring wasn't making contact with the ouside of the RCA. Results in one hell of a noise out of the speaker!! I dont know if these nylon spacers are worth it or not? Maybe I'll just eliminate them. The idea I had was to try and keep a common ground point, ie star grounding through the VTA board. Not sure if its worth it, though.
Another thing that could cause a poor grnd is the spacer screws on the VTA board. I found that not only tightening the hex nuts in the bottom is necessary, so are the screws on the top of the board. Seems that when I backed the nuts off on the bottom the screws on the top also spun loose. I thought this was my hum problem, but no cigar. It was the RCA input.
One more thing, I disconnected the AC ground and it quieted the residual noise to virtualy nothing. I have an IEC input and I think I'll swap it for a 2 wire IEC, 17 or 18 is the number IIRC. That way the next owner won't be thinking it's grounded (and I get to use a thinner cord).

I just finish rebuilding a pair of MK4's, and have a noticeable 60 cycle hum. I owned a Quicksilver GLA amp, and Mike Sanders said he lifted the ground on the amp for the same reasons you describe. One of the MK 4's is producing a loud popping and cracking noise. According to Bob Latino's trouble shooting guide, it is most likely high voltage jumping to chassis ground, ou have any experience with this? Thanks!