actually i came from the m7 and that one did not had this problem. I did recorded concerts and in realy quiet scenarios with the m8 and the microphone works awsome with noise reduction in every situation except in calls. I noticed that a few days after purchaseing it and bouth software updates that i receved did not change anything in this perspective. In my situation bouth htc`s handsfree and normal microphone, call quality is exceptional at the audio that it sends, but when i`m in a noisy place it also records the backgroung noise as clear as it records me on the phone. I repeat only in phone calls this happens. It does the same with HD voice calling and it does the same now after i changed my carrier and its bands.
I own an international stock unrooted / tweaked version of the One m8. No solution yet
P.S. There is no crackle, whitenoise or any distorsion of the background noise during phone calls. Its clear and loud as i am according to the other callers end.
i`m sorry for my english i speak it fine but my spelling is horrible