turn it off and remove pump make sure its clear then replace and try and see if that works you may just have some air trapped in there try purging or may have somthing from your sump stuck in there ,,, it can be annoying but thats the hobby for ya it drives ya mad mine does it evety night about 12-1 am waking me up and i have to switch off and rest but i will not have that problem by next week because i am moving tank and changing all the sump and pipe work so i can fit a larger tank in its place

and having to build a new unit for it to stand on

so my week off work is filled with stuff i should of done months ago now thats annoying
