Aww, that's adorable! Was the hissing sound real? Put yoru ear to the walls to see if it's inside the walls. Then check where you rwater heater is, make sure it's not a pipe leaking. It could be duct work, or coolant leaking. If you have gas appliances, make sure it's not a gas leak.



I don't want to scare you or anything, but I"m like you, if I hear a sound, I'm going to record and investigate. If you can't find it, see if maintenance can come out to do a safety, coolant and plumbing check.

I wonder if you did a collection of his tweeting if you could upload it to youtube or somethng, do a bunch of them and play them as a playlist for him? Might be easier to just find playlists of tiels singing or any wild birds or budgies. I wish my birds liked bird sound recordings.