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.

http://www.xitel.com/product_gli.htm
http://www.pie.net/sec11sb4.htm

Radio Shack also carries one.