The other day when I started my engine after being laid up a week, as well as the 'normal' rattle on start up, it was then followed by a heavy clunk which I actually felt!

(shock through the car & it felt like the car jolted slightly too!). Now this has happened once before, but it was so long ago I forgot about it.
Has anyone else had this clunk & got it fixed?
That clunk is very worrying!