Is it possible that the injested something. Almost sounds like something in the turbine. Remove the acordian pipes and the inlet tubes and inspect. Try spinning the turbine by hand with the engine off and see if it makes noise. Also, grab the turbine by the center nut and see if you can move it up, down, or side to side. Very slight in/out movement is normal.
......And just as they're about to catch me.....Twin......Turbos......Kick.......In!