I recently added a monster cable HTS1000 line conditioner to my system. When the compressor of the fridge (or any other high draw item) would kick in I would get a hum through the speakers. The HTS1000 has removed all noise through the speaker, dead quite. It has a stage 2 filter, as I understand this effectively isolates the HT system from the rest of the electrical system in the house. More expensive conditioners also provide isolation not only between the HT system and the rest of the house but between the various components in the HT system. At around $150 I have been very pleased with the HTS1000.

my $.02