A100 with a hum

[CousinGJ@aol.com]

     I recently purchased an A100. There is a small problem in the percussion
circuit. I'm hoping someone can help. There is a low frequency hum that is
always present (the pitch of the hum is the same as B1 played with the
fundamental drawbar pulled). It completely disappears when percussion is
utilized. More specifically, first I select the B preset key of the manual
and turn the percussion On/Off switch on, no drawbars need be pulled. The hum
continues until a key is played on the upper manual. The percussion harmonic
will be heard appropriately and with its decay, so too will the hum decay,
and remain silent until the depressed key is released. Then the hum returns.
When other preset keys are selected, the hum is always present. I feel the
problem is in the percussion section of the pre-amplifier.  Is this a simple
or complex problem? If I can't easily fix it, should I bring the pre-amp to a
repairman, or do I need to have a service call made to my home($$$).   Also,
I have a Leslie 147 and want to adapt it to the A100. I understand I should
use accessory kit # 7271. Is this something that just requires a few
solderings and carefully following instructions, or is an experienced
technician needed?  I will appreciate any help.    Thank You.  George