On the subject of Ground Isolators: What exactly are they, small transformers?

Proper ones are optical isolators. They convert the audio signal from DC hardwired voltage to optical and back again, effectively severing the path for the ground loop.

This works in pretty much every case. However, it is yet another stage of conversions for the audio signal chain, and as such, there is some audio quality sacrificed in the process.

For instance, the one you can get at Radio Shack specs a frequency range which effectively removes the lowest frequencies from the audio signal. For some people, this would be an unacceptable trade-off. There have been other isolators mentioned on this BBS that are supposedly higher quality than the RatShack ones. If anyone can provide me with an online link to where you can buy the higher-quality ones, I will add that information to the FAQ.

Something to keep in mind: Opto-isolators cost money and are, in most cases, not needed if you could simply locate and fix the ground resistance. Using an isolator is a quick and dirty fix, putting a band-aid on the problem without solving its root cause. Why pay money for something you didn't actually need?