watchman goby, peppermint shrimp, a cuke, couple of snails and somehow a hermit.
To answer your question about water noise, I just use multiple overflow standpipes. The primary one has a gate valve on it to adjust and create a full siphon with the water level just under the overflow teeth. This makes it dead silent. The secondary standpipe is just about 1/4" higher in case the primary gets a snail or something in it. There is actually a third emergency standpipe just because I have a bunch of holes, but only really need one backup.