Upgraded MP5 firing with high pitched, grinding noise!

[webtek23]

I own 2 TM MP5's. I just upgraded one with a M100 spring, metal bearings, and shims. It fires, and at the appropriate velocity, however, the sound coming from the gun makes me cringe. It has a much more high pitched noise coming from it, more like a DEEEW, instead of DOOO. Is that normal for this kind of upgrade. It also has problems firing consistantly. Sometimes it will stick back with the spring partially compressed when it failed to fire because I released the trigger too fast. The grinding noise makes me think that something is wrong with the motor placement or even with the gears themselves, however, since they were just shimmed I doubt it. Comments would be great. Keep in mind that the upgrade was done by myself. I have done many other upgrades and have opened my fair share of mechboxes. This particular unit was used though, so there may be a much deeper issue causing the problems.

[eel one]

it sounds like the gears are shimmed to thight and/or the motor are to far into the mech box. If none og this is the issue. Try aligning the gear again much noise are caused because the gears are not alligned properly, mostly between the beavle and the spur gear.

[CDN_Stalker]

I'd say tweak the motor adjustment screw as well. At times one might screw the motor plate on a bit tighter or a bit looser and not notice, causing the motor to sit too far in or not far enough, causing the screeching gear sound.