I run internal
power filters on my tanks. You can't hear them unless the water outlet is pushing water over the surface, or the water level drops enough. I'd echo the question of what size is the tank? and What type of inhabitants? Based on your past posts, is it the 10 gallon?
I use both of these types
Aqua Top Eliminator with 7w UV. The UV light is not required to function if you prefer not to use it. You can remove it all together if needed.
--There is a flow control on the spray bar to adjust the strength if you have weaker swimmers like
Bettas or
guppies. Cleaning is a little trickier as you have to fully remove the filter to clean it but overall, isn't too difficult.
Oase Bioplus. They are sized for filter "cartridges" attached. ex the 50 has one, the 200 has three. If you have the tank space, having one with at least two compartments is nice as you can have the sponge, polishers,
bio balls, etc. If you bought the 3 compartment, you can remove them and run what you need. Ex. the 3 compartment will still fully function with only 1 attached. Like the Aqua Top, it also has a flow control but has two forms of outlet, a single "jet" and/or multiple small ports like a spray bar that, if placed in the corner upright, would spray across the back wall, and the side wall. You can also adjust to use one or a combination of them. Cleaning is easier than the Aqua Top as the filter housing is magnetic, so you don't have to remove the whole filter every time to clean. I don't use it, but there is an optional
heater for this filter if you need to save some additional space.
I've not used them but have seen them for sale. The
Aqueon Quietflow internal power filter (AT10, AT15, AT30, AT40) series may be worth checking into. Like the two above, they are fully submersible which should make them nearly silent.