Yeah. I had the exact same problem.
I have inserted a few strands (like 2 - 4 etc.) of a toothbrush into the bottom mic hole very carefully and slightly rotated them inside, in order to wipe any dust accumulated inside this hole.
And it works like a charm now.
Be careful. Do not harm your mic while trying this. You may puncture it etc. I don't know the risks exactly, no guarantee.
Try it at your own risk.