Interesting one, I got batch 2 I believe. By hand they make a weird rattling sound when I spin them (makes you think of lose magnets), in the air they have a screaming noise at mid throttle and higher, they are, in short, the most worrying sounding motors I own. If I just tried spinning them by hand and was new (or perhaps wasn't so stupid) I may have been put off and / or sent them back. In the air i don't have any other motors that are as smooth or locked in, my f40 pros may match them, but they really are good, it may be the escs running dshot1200 at 42khz pwm are helping, but they have the torque for any 5inch prop, transition speeds are unbeatable which is what is making them smooth, loads of power but actually decent efficiency for acro (if you don't live in the last 20% of the throttle band for the whole flight). Really like them