From somewhere I heard a bang then a clatter. TV was on so couldn't locate it from sound. Looked outside, as it's quite windy, then went upstairs. My back 'bedroom' is actually an indoor shed and I keep paint etc. in there amongst many other thing.
On the floor, sticky side down (of course), was the lid from a can of metal paint from Aldi. The can is still full so there wasn't much room for a lot of gas to build up. The lid had about 40mm of its rim folded down and was also distorted enogh to need a 1lb. persuader to get it back to shape. As the can is under another shelf it must have flipped up edge first and had just enough space to do so.
It's a bit worrying, especially as the sun doesn't shine in there and the temperature's not varied much since I bought it. If the can had been half full the extra gas and lower mass could have resulted in a mess.