We recently had a Toto Nexus installed in our bathroom. Since the installation it has made a trickling noise after the refill as the water is leveling itself. Toto says it is "normal" but it is rather loud - doesn't sound "normal" to me. It lasts 11 seconds. It is not a drip, drip, but more of a trickling/gurgling sound. Is this the same issue with the plastic unifix piece or could it be something else? Do all Nexus toilets make this "after-flush" noise?
And the length of time and the sound level can vary slightly depending on room acoustics, the way the home is plumbed and with what material and how level the home is.
It's the sound of water leaving the bowl.
I'm pretty sure your tub does the same thing.
It's a little different, but at the end of the day, it's just one more appliance that either clicks when a switch is flipped, a motor that whirrs while closing a garage door, a refrigerator that bangs the pipes when the ice cube tray refills in the middle of the night, or compressor hum when the motor kicks on, and the cold air return on the furnace. When the home warms in the day and cools at night wood will make creaking sounds too. Lots and lots of normal sounds out there. I come from a family of seven. I used to practice my electric guitar in the same room we watched TV in, unplugged of course. Didn't seem to bother anyone.