Hi guys,
First of all, I want to thanks everybody for your help and advices. The VAF community is so great. We have to keep going on and continue to support each other.
Good news!!! Problem solved last night. I went to the airport and started by rechecking all the connections and tapping every screws. Didn't help as everthings were already all right. Then, I realized with somes tests that the problem was from the radio. When I turned the radio off and was using the intercom only, the problem disappeared. As soon as I turned the radio on it was like if my micro was permanently activated. At the begining I had doubt that it could be the micro gain because people who experienced mic gain problem reported it was only when they activated the PTT.
Finally, I removed the radio completly from the dash because Microair doesn't have any mic gain adjustment in the menu. You have to adjust it by a screw on the side of the radio. I lowered down the mic gain and tested it and what a surprise. My comm has never been so clear. I just wondered why the mic gain disadjusted by itself after a year and a half of good work??? Anyways, I wanted to share my experience to all of you. If it can help only one pilot who experiment same problems, the mission is accomplished.
(sorry for my limited english!!!)
Pat