60 Cycle Hum

I have cleaned up the area around my stereo

[Hafler DH500 Amp, Tandberg 3002A preamp, Dahlquist DQ 10 speakers, Cambridge Audio DacMagic, Apple Airport]

and removed or turned off a lot of other home electronics. However, I still have a low level 60 cycle hum. The amp was examined and tweaked by a reputable repair shop, but it seems to be the source of the hum, which is not all that annoying except for the fact that it exists.

Is there any type of filters I can add to the amp or speaker cable to eliminate this hum, or is this just the natural state of things with classic analog systems?

Thanks in advance