Water flowing back out by the intake? Most have an overflow around the intake that allows bypass back into the tank to prevent spillage.

It's happened on every hob filter I've had. I've always treated it as an indicator to clean the media (always in tank water), though it's closer after each cleaning. Even using nothing but plain felt or bio sponge they'll still overflow from time to time - Though I have one that will almost constantly have some overflow past the media. (30+g filter on a heavily planted 10g tank)

If you'd like to quiet down the filter a bit, fishing line and a spare bio sponge work well. Simply tie the sponge around the hob across the output, it cuts down on noise substantially. The fishing line will thread right through the sponge without much effort, you can trim both down to your liking. It does cut down on surface agitation. (Better for planted tanks, not as great for heavily stocked tanks)

Hope it helps.