I agree with Caleb on this sounds like the tank wasn't cycled causing fish to die and get sucked onto the filter strainer , but yes I have seen some filters with a very powerful suction as a mater of fact I have one
there is a quick fix to that filter, it's a perfect fix all it is is a 1x2 piece of square foam I cut a slit through the foam center so I can put the filter strainer into it , i replace it once a month I think there like 2 bucks