Weird sounds from ebike controller and motor.

[eleusys]

Good day,
I am working on e-bike controller from China of 3 kW, trying to make it run. Unfortunately, after start, when it reaches ~5 A consumption it makes weird sound and stops spinning. I release throttle and it works again. I have 48V lead-acid battery and was wondering, maybe some1 had similar issue? Here is short video.
youtu.be/epHPdVD3NyQ

I wonder, what can it be?