voice issues

Hi guys

I am having serious audio issues in Flight Sim x dELUXE. My mic works fine in general voice chat eg msn yahoo but wont in here. I have been told to push caps and shift caps they can here me ok i hear them ok but there saying my voice is crackly. I have gone through 5 Mics trying to fix this has anyone a clue if there is a setting or what i may be doing wrong.

Thanks
Jazza

ps brand new logitech mic over $200 worth has to be something.