I get exactly the same with my Juwel. I took the first one back thinking something was wrong with it, but this one does exactly the same. I have to move it slightly to stop it, but that only stops it for a little while. Very annoying. Juwel told me they had never heard of it happening!i have a juwel heater that knocks on the glass sometimes as i heats up it causes a little water movement, just enough to make it move slightly. i often have to move it slightly and then the knocking stops.