Dont mean to open a massive can of worms but...............

Does the compressor wheel really stall? The way i think of chatter is if you spin a fan and blow through it the wrong way u get a whirling noise. If the fans stopped or "stalled" and you blow through it, it makes very little noise....

My point is, i dont think chatter comes from the compressor wheel stalling, more likely air rushing past it in the wrong direction and the blades chopping the air as it goes past!

ok i'll get my coat