I have one of those Aqueon AT10 quietflow internal filters in a 5 gallon tank and as said above it is VERY quiet. I also rubber banded a piece of foam over the output because it was too strong for my betta.
I have an Azoo palm filter in another 5 gallon tank. It's not as quiet as the Aqueon and I was having a little trouble with noise from it but it seems to be doing okay now. You may need to fiddle with the cover a little to keep it from vibrating, and I think it also helps to keep the water level close enough to the output to cut down on loud water trickling noise.