low level hum

So the other day I noticed on the lead out track a low hum.I can also hear it on the lead in. It is not noticeable when music is playing and disappears as soon as the tonearm is lifted.I am using a Pro Ject 2 xperience with a dynavector 17d3 cartridge into a PS Audio GCPH. What is going on I never noticed this before. I've had this combo for about 6 months now.
So it seems the hum is coming form the speed box. Hum disappears when it is set to 45r.p.m. and when it is totally disconnected.Has any one else had a problem with the
speedbox II. Is this a defective unit or is this a common problem?Will the speedbox SE or the music hall cruise control 2 have the same problem?
I have the identical problem with my Speed Box 2 / mmf 2.2 TT. I have a call into Music-Direct - we'll see what they say. The hum is gone with the original music hall power supply. I am using a Shure V15VXMR cart.