Hmm... Problems that go away by themselves tend to come back by themselves.
If it was everywhere - recording, stream, headphones, appears on the meter, etc. - I'd say that you had an analog mic cord that was picking up interference. That's not insurmountable - the pro audio world solved that problem decades ago by using balanced cabling - but you would still have to change some gear though.
But if your 'phones are clean, the mic is fine. The meter probably doesn't show it either. Unless you don't actually have that mic in your 'phones: then it could misbehave and you might not know it until you played it back later.
Since it's a headset, I'll also mention this: I was talking with the tech volunteers at a church that had just upgraded their system, and they were wondering why the pastor's headset mic was "scratchy", "distorted", etc. They were wondering what kind of processing they should put on it to get rid of that. I took one look at it while he was wearing it and said something to the effect of, "Just move it a bit. He's blowing on it." So you might check that too.
