Depending on the version on Android T-Mobile has released a Software/Firmware update that may fix the problem. When I can i will post a link to the .zip file for the 2.3.X update if you do not have it already.
There's an app called smc fan control it should give you a reading on how hot the cpu is. If you it is that you could open up the case and try to use compressed air to clean up out some dust, and I or makes the fans run at a higher speed by increasing the rpm speed in the app.
