@Kallela

Check page 51 and 52 of N9's user guide: http://nds1.nokia.com/phones/files/g...a_N9_UG_en.pdf

The noise-cancellation is ONLY for normal mode. Like I said before, it doesn't work if you are on loudspeaker or if you put the headset on.

However, YOU are partially correct; the mics itself are reversed. While on a normal call, the primary bottom mic is used and while on the loudspeaker, the secondary back mic is used. But noise-cancellation only works on normal mode.

@foredoomed

Most people with this problem reported it to be solved if they just used compressed air to clean the debris in the mics. Nokia care probably won't do anything with an N9 and it would be a waste of money to try. Since you said the problem occurred a few days ago and wasn't there since the day you bought it, it's either a software issue (something messed up the audio drivers in the second mic) or a hardware issue (maybe you bumped your N9's back real hard or it fell down or something).

Like I said, first try reflashing it and see if the problem disappears. Then try cleaning the dust inside. If neither of this work, Nokia care would be the last step.