Even without a stethascope it sounds like a whiney big blower even at idle compared to the Gen 3. Not sure if that'* normal.
What is there to rebuilding it besides replacing bearing. It has a rebuild snout. The rotors look good.
Will the bad bearings cause KR
Maybe Zilla porting got some contaminants in the bearings even thought they were taped.
I'm gonna run it without the belt (SC turning) tomorrow to see if it still produces part throttle KR.
I have a concrete pour in the morning (taking the day off work for overtime) for my new backyard storage shed, but may have time in the afternoon for a trial.