It does seem to be trying to stabilise.
Check props on correct way up.
Did you use the set up wizard ?
Are you using attitude or rate flight mode ?
Is 'zero integral at low throttle ' ticked and saved ?
Are you using default pids , and response rates ?
Are giving any input apart from throttle ?
Meanwhile no harm in re doing level calibration on attitude page , ( and check orientation is 0,0,0 on that page )