I'm not really concerned, I've heard him make this noise in the day like when I'm petting him or he's being crazy. Yeah I cover his cageSince you're concerned, see a vet..just to be on the safe side
Do you cover his cage at night?
It sounds kinda like a cat purring but more high pitchMy conure will sometimes laugh ominously if I accidentally wake her up in the middle of the night. She'll make other soft noises too. I also peridocally hear beak grinding at night.
Not sure exactly what sound you're describing to say for sure if my babies have done it, but it's probably nothing to be worried about.