Screeching gearbox noise

[RKG]

I have a VFC BAR and have put in a few upgrades recently but for some reason there is a loud screeching noise that I can't get rid of. I have shimmed the gearbox, adjusted aoe and adjusted motor height but the noise doesn't change. I've reshimmed the gearbox several times and always shimmed from the bevel gear but there is no change to the noise. The gun fires fine with a great trigger response and decent rate of fire. I'm just not sure what else to do.

The upgrades I have put in are:
SHS High Torque Motor
SHS 18:1 gears
Guarder reinforced piston
ASG Ultimate Piston head
ASG Ultimate Cylinder Head
M100 Spring
ASG Ultimate bearing sprung guide


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[reedy.]

Where you doing the shimming with half a shell?