Odd query about an odd experience

If the frame was a hollow metal tube a mouse could have got in there - perhaps a dormouse hoping to hibernate.

Nope! We've shaken the frame and knocked it. It's solid tubing. We really truly have thought of everything!

Open it outside then no danger if anything getting onto the carpet.
Get your DH to do it if you're squeamish.
If it were mice there'd be holes somewhere ans scraps of chewed fabric.
By the way, my sister had bruxism and her teeth made a sort of high pitched shreik, like chalk on a backboard.

Bats?

Hannah please look at the posts where I've already said it's gone!!

Just a thought. Did your grandchild grind his teeth when sleeping?

I’m so pleased the problem is sorted if not solved. I assume you now have a nice new mattress.

As a solution to small insects, may I suggest a pet spider. At our old house we would be beset with spiders every autumn coming in from the cold. No matter how many I removed more came. Webs and spider droppings appearing overnight. Every night. Then we moved to this old place and have a resident house spider. Just the one. She’s huge and lives mainly in the sitting room. We can actually hear her pitter pat of tiny toes when she runs across the floor. But there are no other spiders or any other insects in the house. There are quite a few in the conservatory though as she can’t get under the door!

Eek! Sounds scary. We don't have much of a spider problem though. Baz just puts his massive paw on them and that's it. He doesn't know what to do with them after that though so I have to dispose of the bodies

Sometimes it is best not to know what is inside. You can never unsee something and with me, at least, every mattress in the house would possibly have same "thing" had I seen it, but not until the point of dropping off to sleep.

Then I'd be up and out of bed like a crazy woman ear to every mattress in the house at midnight.

Glad you have taken it to the dump, intact.

You would definitely smell mice if they had been in residence for any length of time

Get rid and buy a new one, also just for fun check all your smoke alarm batts...

Onestep, the OP confirmed 3 days ago that she'd disposed of it, so its long gone!

onestepbeyond the noise was nothing like the sound of a smoke alarm with low batteries. It was exactly like cicadas.