"david" wrote in message
om

Please let me know if you have any suggestions for reducing or
eliminating the hum.

So far you seem to have avoided a lot of the usual tricks for managing
ground loops. Here they are for your reference:

http://www.smr-home-theatre.org/Grou.../addendum.html

http://www.epanorama.net/documents/g...oop/index.html

http://www.walrus.co.uk/tech/hum.htm