OK, I understand the ground wire. I tried something similar, I held the metal ground ring of the un-used plug against the computer case. It did reduce the glitches but did not completely remove them. Difference between us is our computers, mine may not be as well grounded as yours or mine may have move components that make noise.

I'm thinking that we may need some ferrite cores, to block any high frequency noise, on the USB cable , my G2 USB controller does!

Greg.