semi ot: ground hum?

["diatom drone" <skincage@infin8ty.com>]

has anyone experienced ground hum when using one of those a/b switches? the
kind i mean is the a/v one from radio shack that has 2 video, L, R inputs
and one video, L, R output with the A/B selector between them. basically i
was trying to rig it so i could have either the audio out from my VCR or 
one
of the analog outs on a SB live going into the "Aux" on my receiver. this
isn't directly related to recording but i figured if i can fix this i can
apply it to similar situations in a mixer. thanks for any help

jon