One thing I recently found helpful, is try unplugging the inputs to your preamp to see if it goes away. I had my TV connected into the aux input, TV's are a great culprits of hum because there antennas are grounded. This solved my hum problem, and it wasn't present with the previous preamp.
Audible Hum
I just hooked up a pair of Clayton M70 monoblocks to my Martin Logan Requests. There is now an audible hum coming from the speakers when the volume is off. The amps are located close to the speakers.Is this the problem? I am new at this and would like the groups help. I did not have this problem with my B&K amp which I replaced.