I was thinking that electret capsules only had a + and - wire, and that the ground is added in the body stage. but I could be wrong. If it stops when you touch the mic it sounds like a ground problem. Just to be sure, you have the High Z set to low, you have switched cables and the hum stays with the same mic, you plugged the mic bodies directly into the UA5 (no cable) and the hum stays with the same mic. If you have the mics plugged directly into the UA5 and switch only the capsules, the hum moves to the other channel? If all this is true, then it does sound like a grounding issue in that capsule. When I got mine, the capsules were really hard to unscrew, so I didn't bother trying to hard. I believe yours were from the same place, and were a new pair. Is it possible that when you unscrewed or rescrewed the capsule, some of the threading broke off, or the capsule is not threading on correctly? If possible could you take a picture of the capsule off the body?