Does excess voltage cause hum?

Not likely that this would be the direct cause of the hum. High mains conditions can cause higher levels of transformer "hum" due to the abrupt increase in excitation current that occurs as the magnetic material nears saturation. The most likely cause of the "hum" is a high noise floor in your equipment. As for a method of diagnosing the specific component, I can offer the following trouble shooting tips. If the level of the "hum" is affected by either the source that you select (tuner, CD, phono, etc) or by the setting of the level control, then your problem is either the preamplifier or the specific source. If it is a constant level, regardless of the state of the above mentioned controls, then it is likely either pre or power amplifier self noise (with power amplifier being more typical). Other trouble shooting steps can be taken, but more specific details as to your system and its configuration would be required. Kevin Halverson

Thanks Kevin. Most helpful! I will be rearranging my set up in a week or so with the help of a pro. I'll let you know if anything changes.

I experienced hum with a high-powered SET amp, and the manufacturer told me that my high voltage is most likely the cause of the problem (it does vary quite a bit...occasionally shutting down my Panamax). I have no hum at all when using solid state amps.

My current system is as follows: Denon AVR-5700, B&W Nautilus 805's, REL Strata III subwoofer, Panasonic A-310 DVD, Monster HTS-3500 line conditioner, Denon MD-1000 minidisc recorder, Harmonic Technology Pro-9 Plus Bi-Wire speaker cables, H.T. Cyberlink Platinum Coax, H.T. Truthlink analogue, H.T. Pro-11 AC power cord, Synergy Rack system, Toshiba TW40F80 widescreen PTV.15amp ac outlet, and one 20 amp dedicated outlet. The Panasonic DVD player is temporary. I will be getting either the Sony DVP900ES DVD/SACD, or the Pioneer DV-37. Perhaps their is a weak point here that I have overlooked?