Ground loop isolator question ?

I think I've a ground loop causing speaker hum. I've my HT pre's front L/R connected to the HT loop of my stereo pre and whenever I switch to HT, I get the hum. If I change the source to cd on the stereo pre, no hum.
When I do a on-line search, there are several GL isolators, what should I get ?

Here are some links. Any others ? Appreciate any suggesstion.

Radio Shack also carries one.
I've had some hum issues in my audio/video system that was related to a ground loop between electrical ground & the cable TV ground. Anytime I disconnected the cable TV the hum went away. Used a jensen inline transformer on the cable & it solved the issue
Thanks, Hhiggins. I thought about cable causing the hum also but did not check that yet. I'll check that.
also check out Jensen Transformers...they have several products