it is very similar rpm ranges yes, but I tested both motors individually and they both do it, its definitely not just one motor.
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my old battle hardened 6374s made no abnormal noises at all. its strange and unfortunate that these ones do using then same esc.
Hm well, that being said, my FS motors have a resonance at super high rpm as well, similar to yours, but not as loud. I don’t go that fast and can’t hear it under load though
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Mine sing to high glory in the midrange. If I cruise at that speed I get paranoid of pitbulls jumping fences and chasing me down . The last chase still gives me nightmares at high speed
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I have m1s and FS 6374s and it sounds normal to me, make sure your backlash isn’t too tight.
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My m1s are queit compared to the AT drives. Same motors on belt drive are quiet. Its definatley the AT drives that resonate at a certain frequency that kinda hurts your ears but it goes away when you go faster or slower. I was thinking I need mo grease
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both motors do it regardless of whether or not there are gears. the motor spinning alone makes that higher pitched grinding type sound at a certain rpm range
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Tom said my board sounds like a laser beam
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I got the same thing. My guess is when I cut down the shaft to fit the gear drives some metal shavings got into the motor and that’s the cause 
can you look from the side to see if the can is expanding during this event? Should be very obvious if so
I bought a board here on the forum that had same high pitched noise at certain rpm. It turned out that the motors were in very bad condition - lose shaft, bad bearings, lose cracked magnets, bend clip. I’m not sure what had caused the sound exactly since those motors are done, but there is most likely something lose in the motor. Disassembling and inspecting motors wouldn’t hurt if you have time for that.
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Mine have made that noise since day 1 - not saying it couldn’t be what you mentioned, but it’s also not necessarily bad
I think some are just louder than others
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yeah I didnt cover the motor when I cut the shafts, im sure there is something in there.
I can try. I will update
i don’t think its necessarily bad, its just annoying.
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My pinions are offset from the spur gear by alittle. I wonder if that changes the sound. Only one is offset alittle.
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Second this. I posted several videos back when we did the first group buy, shortly after they launched. Mine had this loud squirl at 87-89% duty cycle
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I have the same thing with a pair of 6374 motors.
It screams like hell at some rpm. Really annoying
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I’ve had this on seperate sets of maytech motors before. Really strange
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Same here. Chocked it up to being an harmonic imbalance in the motor. Mine sound no where as bad as OP’s does though. Could be more than just an imbalance. Or just an aggressive imbalance.
I’d pull it apart and check the inside.
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I know this is an old thread, my brand new flipsky 6354 BH motors have the same resonating whistle at a certain rpm with belts and without. Drives me nuts.
It’s annoying enough to consider shelving these and buying a different brand motor.
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