Static Problem when recording vocals

[Filmmaker123]

Hello, I am using Pro Tools 10.2 on Mac OS X Lion with the Profire 2626 as my audio interface. When I record vocals, about halfway through the session I get this "pingy" static over the waveform. When I stop the recording the static goes away and only occurs as the artist talks through the channel when it is on record. When I turn the channel off, no more static. When I turn the channel on, there is no static until audio comes through the mic. I know it is not a problem with the mic because it works perfectly for half of the session. I am not going through any pre-amps. My set-up is going from the mic into the ProFire 2626 which goes into my Mac Pro via USB. If anybody can help me out it would be greatly appreciated. Thanks!