Everything sounds fine on my end using handsfree, but anyone I call/connect to, says they can't hear a thing, or is very hard to understand.
Car is completely stock save for a EC tune.
Is it the location of the car's mic?
A software problem? It's been the same on my iPhone 4s and iPhone 6…
Kind of a pita that it's an expensive enough rig, and sad my old '07 Ram had better sound quality than this...

I hate to disappoint you, but it's only going to get worse when the headers go onto your car...

Btw, when are you getting them installed?

Yep, BT is bad in this car. Much better in the 550i I owned prior to the C63. Are there any upgraded microphone or sound boost options?

Well that's good news
Jeff, hoping to have them up and running in a month or so. Went on a couple holidays, taking some time to get caught back up at work. Once that's done then turn attention to it.
After having yours for some time now, would you do it again? Change anything?

Yup I don't know why it's so low volume. I can barely hear sometimes myself, and I always get complaints about the other person not being able to hear

Have you adjusted the reception and transmission volume in the BT? It doesn't do much, but it helps some. Go to the phone screen, select the options next to the name of the phone, and increase transmission and reception volumes.

I don't use handsfree calling much as I would just rather not talk while driving, but when I have I never got any complaints that I couldn't be hear. Maybe I'm just a loud talker.

I did notice though that the BT, etc was much better in a facelift C i had as a loaner from the dealership

I have a 2010 C63. I use the Bluetooth daily with an iPhone 6+ and have had zero sound quality complaints. Much better than my previous ride.

Get your butt in gear and get caught up with your work!

I've had the headers since the beginning of the year. I have been loving the headers the whole time I've had them installed. Had I had known that it sounded this good, I would have bought them a long time ago.