cannister filter problem

[millenium]

I just switch a canister filter previously for a 200L tank to a 70L tank. The filter will tend to give out rattling sound after operating for 1-2 hours. This seems to be due to the impeller working with less than optimal water level in the canister. At first I thought because I have placed the canister too high on a chair. But after I place it on the floor, the same problem persist. The impeller had just been replaced with a new one when I re operated it.

Could it be anything to do with the level of the inlet and outlet points in the tank, length of the hose or water level/tank volume, can anyone experienced with canister advice me?