[jdavia]

A ground loop isolator may help in some instances but it is better to find the source of the ground loop if possible.
In my case I had a system hook-up that was noiseless untill I re-installed everything in a new cart. I had a terible hum. I carefully checked every connection, all were ok.
Then I discovered one of the screws used to hold the pre-amp to the cart was touching the case that operate the lights. That was the loop that created the AC hum. So placement of the components, checking all line cords for a good ground connection are important to reduce or eliminate AC hum.
To me the best cure is to eliminate the source. Anything else is a work around.