3rd time in a week this has happened. This drain outside my kitchen is also where our sink/washing machine etc drainage flows

Ideas so far:

• Foxes or squirrels attracted to some smell from below (we can’t smell anything, and I imagine you’d need something more dextrous than a paw to lift it out)
• Killer rats escaping the sewer below

Those 2 grates are 1 lightweight plastic one and a broken iron one, which are usually just stacked together.

My guess would be rats. We had similar and I actually saw one emerge from the drain. I ended up fitting a rat flap on our main sewage outlet – basically a one-way valve that’ll let them out to the sewer but not back into your domestic pipework.

Vampires

I was going to say gas… But the grates look pretty light and they have holes in them…

So.. Embrace your new furry friends.. Or stick /screw the grates down appropriately.

Is that Tom, Dick or Harry?

Rats. As above fit a non return valve. You can get ones that just shove up the pipe where it discharges into the manhole. Allows flows out but does let anything go back up the pipe.

This sort of thing, but you can get them cheaper.

https://www.screwfix.com/p/metex-buffalo-nrv-rodent-non-return-flood-defence-valve-110mm-4-/408KX?

Roland.

Infant mutant ninja turtles

Edit: Damnit! Beaten to it …

pennywise the clown

They were called teenage mutant hero turtles in the UK… As apparently ‘ninja’ was deemed to be too violent of a word.

That’s my fun fact for the day.

Could be Pennywise. That freaky bastard can squeeze through small places like some sort of nightmare hamster. Are there balloons floating about your garden OP?

Clangers

Infant mutant ninja turtles

You must mean Splinter, by the sounds of it

Mutant turds. They are evolving and now have developed limbs with opposable thumbs so can easily move things.

Caveat: I have had more than one glass of rather nice Portuguese wine. Also, I cannot spell Portuguese easily. It’s a really difficult word.

🤷🏼‍♂️

Water?

Looks like it could be blocked to me

I’m with Funky Dunc, there could be a partial blockage and when the washing machine empties it backflows and pushes the grill off………………

She’s absolutely chokka mate! FIRE UP THE JET!

When we had an issue with surface water drainage, it would back up and push the grate off every single time.

You could always see if you know anyone with a trail camera and it will take photos of any movement to rule out rats etc?