problem with microphone in the phone sip-t22p

[alexey127]

Hello . I have about 20 phones sip- T22 , 6 months everything worked perfectly . the problem started with one phone . when picking up the phone for a call that a friend could hear perfectly, but my voice was not heard or had heard noises and creaks . When I talk handsfree no problem. I changed this phone , connect and configure a new phone , I installed the latest firmware on the phone and the problem reappeared . the device has three lines, each line set to different operators , the problem remains on every line . I tried to install different firmware , but it does not help. computer connected to the phone , it can be a problem ? I tried to disconnect the computer from the phone , did not help . I think that the phone will burn something , but can not figure out from what?
I do not want to burn another phone . please tell me what to do ?