TD200

I have a 200 series Turbo deisel with factory fitted bluetooth ...the unit has been replaced 3 times. I can hear people no problem but all they ever hear from me is a garbled message. Re pair and it works fine for about 3 hrs and then starts agaon. Have had the following phones and been the same with all of them. Nokia N96, Nokia e65, iPhone3g, iPhone 4, iPhone 4s,. The services guys tell me I just need to adjust the mic volume up or down but it doesn't make any difference. Would like to know where kschoelpple got his unit from???