i dont know what "grounded" is, but i guess that's not the problem cuz i tried it on other amp's and the problem was still there.
with pictures:
"my" guitar:
http://images.amazon.com/images/P/B0...CLZZZZZZZ_.jpg
the "jack entry" where the problem seems to be (not my guitar just got this out of google) :
http://www.nealmoser.com/images/11%2...t%20jack.j pg