That's EXACTLY what ground loops do!
Humm/buzz is the result !
My electronics guys always told me to rip the third prong off ALL my cables except ONE. There is no need for the ground wire on each piece as long as they are all in the same outlet. I never did this, and I've never had a problem either, but it comes up every now & then if I forget and use two different sockets on each side of the stage. Now - I only use ONE outlet from the house, and run everything through that source.