[bschwindHN]

> My guess is just wax and gunk getting to the external microphone mesh over time, but there is no way to deal with it

I haven't tried this myself but someone on reddit mentioned you can use blu tack (sp?) - press it on the external mics, then pull off to clean it. I imagine it works but as I said, haven't tried it personally.

[randallsquared]

I have tried it (and done this more than once) -- it does work, but it's not quite that easy. You have to fashion the tack into various shapes to get into the crevices, and it has taken the better part of an hour to be satisfied with the result each time. Still worth it.