ok so this has been bugging me since yesterday. built a new 3.5inch ultralight, everything looked good on the bench, motors all spun up clean, no weird noises. took it out for the maiden and it flew ok-ish but the whole thing just felt kind of... mushy? hard to describe. like control inputs were there but the quad felt like it was always slightly fighting itself.

got home, plugged into betaflight and the gyro traces looked horrible on motor 2. there's this consistent oscillation that doesnt go away even at low throttle. the other three motors look clean. i re-seated all the motor screws thinking maybe one was loose but no change. motor 2 feels smooth when i spin it by hand but maybe slightly less free-spinning than the others? could be nothing.

running 1404 motors on this thing, relatively new to smaller builds so im not sure if 1404s are just naturally noisier or if i actually have a bad motor. didnt crash it, was a gentle maiden in a field

swap motor 2 with one of the others and see if the problem moves with the motor or stays on that arm. that'll tell you pretty quick if its the motor itself or something mechanical about that arm/mount. 1404s are pretty smooth motors generally, they shouldnt be causing gyro noise like that out of the box. could be a slightly bent shaft from shipping, ive gotten motors straight from the factory with shafts that were just barely off and it showed up exactly like what you're describing ? fine by hand, terrible under load

also check if your motor wires on motor 2 are maybe too tight or routed weirdly and transmitting vibration into the stack. sounds dumb but ive chased a vibration issue for two days before and it turned out one motor wire was just pulled taut against the frame and acting like a little antenna for noise. probably not your issue but worth looking at while you have it open anyway. the shaft thing is more likely honestly