I'd say its the 4 wheel.
Mine us the same, i gotta replace my actuator. But mine only does it when my 4x4 is engaged. Your doing all the time sounds like a vacuum line leak. Possibly something happened when you installed the exhaust maybe?
Just noticed you had the tick before the exhaust, but i still believe its in your vacuum lines
Last edited by ellis4pa; 10-19-2012 at 01:16 PM.