Hi all. I have a JoeMeek VC2 that I use mainly for vocal tracking with a U87 and acoustic guitar tracking with a KM84. Both combinations are nice and quiet. A few days ago I put a Shure SM137 on that pre and I get what sounds like a 60hZ hum. I switched XLR cables, I switched lines from live to control room, I switched patch cables that go out of the VC2 and I switched to a second SM137 - hum is still there. I even swapped the tube out of the pre. Hum is still there. If I put the U87, KM 84 or any other mic in the VC2, it's quiet. If I put the SM137 into my 003 rack pre, it's quiet. All connections are balanced. So why is the combination of VC2 and SM 137 "hummy"?