I bought a Behringer B5 condenser microphone a couple of years ago to record my acoustic guitar. Add in a second dynamic mic I already owned and a little two channel USB preamp with phantom power and it sounded really nice.
Then after a few months the condenser mic started picking up some interference. It was a weird kind of rumble but with a kind of radio tuning sound, and the odd pop and click.
I tried changing channels, switched power supplies and cables but nothing helped.
Finally I came across a forum post describing a similar problem with the cause being humidity. Apparently condenser mics don’t do well in humid conditions and my office is a little damp. I’d left my mic out of its case a couple of times in these conditions and it got damp. The silica gel packet that came in the case should have been a clue.
Anyway, I popped my mic in my electric oven set at 30C, left it for 30mins and now it’s as good as new! Phew.