It sounds like a parrot.

Earlier, I mentioned that I had a joke but had forgotten it.

Then, I heard it again.

To a girl who has been in the Amazon rainforest as a missionaries' kid, and later as a grown-up missionary, it's a fairly well-known sound. It starts with a gulp; then there's a squak, followed by an almost-hiss. It's an Amazon Conure, a predominately-green parrot with either a yellow or red spot of marking.

So why am I hearing it at a house in Missouri? I keep looking around.

Finally, I spot it:

An exotic automatic air-freshener! Geesh, you really had me going.