Scary Mum you had! My old Scots Granny aye said it was the angels moving furniture - but I think that was meant to reduce the fear factor. Didn't really work though. Then it became exciting to watch the lightning and count the beats till the thunderclap.
She could be quite formidable.
My Gran though used to say the same about furniture, only it was God moving it around. Much better, even if didn't work either.
I had to get on top of my fear though when I went to boarding-school because all the other kids seemed to enjoy thunderstorms and I didn't want to appear a scaredy-cat, even although I was shaking inside.
We also used to count what we thought were the seconds between the flash and the thunder clap in the belief that it told you how far away the storm was, i.e. 1 second = 1 mile. We weren't far off the mark though because it seems that 5 seconds = 1 mile (all tied up with the fact that light travels faster than sound through air).