Hello everyone, my drone runs APM 4.4.4 firmware. When hovering in Loiter mode, the aircraft always maintains a tilted attitude with a noticeable pitch angle, yet the two rear motors have higher PWM output. I would like to ask if this is caused by tilted motor mounting. The flight controller is installed horizontally, and the HUD in MP shows level when the aircraft is on the ground.
First guess would be wind? It needs to roll/pitch into the wind to hold position. You can check attitude in alt-hold mode. It should be level but will be pushed away by wind.
Try look the fc alignments ,recalibrating level with compensating to our unwanted pitch (not ideal but works like a dream in most cases)
if still no change look at the individual motor tests ( some motors/esc fault could cause it ), look if all the motors spin in almost identical speed for the same throttle percentage
Try it out and if it still don’t work share some actual photo of the build and find me here
Best of luck
Look at weight distribution. It causes some motors to work harder than others
I conducted tests in a windless indoor environment with LiDAR as the positioning source. The drone drifts forward rapidly after switching to AltHold mode.
I suspect the issue stems from my motors or frame not being perfectly level. After mounting all motors with a slight forward tilt, the drone’s pitch-up angle has decreased significantly. Since the frame is 3D-printed and assembled by myself, there may be certain mounting and assembly errors. 
Assuming no mechanical issues, I would re calibrate accelerometer to set level. Otherwise You have some fancy motor mount arrangement (by design or accident).
Even with uneven mass distribution, resulting in not equal motors output, drone should try to stay in place in alt hold mode and keep itself level.
Not sure what You have in mind by “lidar as position source”.
BTW - can You post a photo, or link to 3d model You used?