Can someone help me with this motor issue?

Hello everyone,
I bought this fatbike new from Alibaba. It directly came with this problem. Motor and gear set (clutch) is already replaced and the problem the same.
– It only happens after acceleration (sometimes not always).
– During driving away from 0 ,or after hard brake, or when climbing a little hill.
In this short moment the bike makes an insane amount of noise. And the motor lacks in support in this moment, after this the motor works normal.

Does someone know what the problem can be?