[madjim- with the Lord]

Hey Carl,
Bob, Dale and Mark are all correct. Since the problem went away when you lifted the ground (this is what the three prong to two prong plug did) there is a ground loop somewhere. (this is what Dale explained, the path of least resistance)

When ever you set your system up, be sure that EVEYTHING is plugged into the same power strip which will go to one outlet. Since you have the same problem at home it leads me to believe that the ground loop may be occuring in your system somewhere.

There are plenty of power conditioners availabe but I have been running PA systems for more years that I like to talk about and find that ground loop problems can be delt with by following this one simple rule. I have never had to use a power (or line) conditioner, I just eliminate the ground loop.

I Hope This Hekps.

Jim