Hi Whart...is this the Tripp Lite unit you mentioned?
http://www.amazon.com/Tripp-Lite-IS1000-Isolation-Transformer/dp/B00006HPFI
To clarify about what I was describing (hopefully this will be of value to BDP, too) ... it's not an audio related pump but rather the house heating system heat pump coming on and causing a very brief voltage sag that the APC corrects. Fortunately, no noise is heard through the audio system when this happens. Funny though, a nearby closet light switch on a totally separate circuit WILL cause a nasty snap audible through the system if it's turned on while the gear is powered up. Put a piece of tape over the switch as a reminder and I just don't flip it when the system is on.