The sound only occurs under boost..I believe if the compresor was surging the response would be somewhat erratic.. The car pulls very nicely up the scale..The other point on compressor surge , AAM did over 30 dyno pulls with no problem.. Thought about a leak since only getting 6#'s but I convinced myself the D.C Headers allow more gas flow than stock preventing the 8#'s.

 

Headers will decrease boost a little . What type of cats do you have ? If they are OEM , that will decrease flow alot . And you should still make full boost . At one time , I had headers and open pipe . I still made 7.2lb's of boost . I put on Crawford cats and got all the boost back .