thats because its a greasy mess inside

dust is cludding between the top and bottom gray speaker grill and the housing.

buy new grill on ebay , get the original off ,clean gently with pensil and vacuum cleaner.

ensure all is clean and dry , stick on the grill , vôilla its done ,your mic,s are like new again.

The lenses are actually in the back housing.

I just finished a complete outside overhaul with new

front and back housing and lcd replacement due to cracked screen.

It took me some hours , but wel worth it.

the parts cost me 38 euro and came via the mail in two weeks.

Thnx IFixit for the great tutorial in the background.

best repair site ever!

you forgot about the topspeaker, its in the fronthousing , and its a mother to get out!

be carefull