I haven't flown for a while but I remember that there used to be a sharp "rap rap" when first taking off, like a car travelling over a bridge seam. First time I heard it I thought the ass had hit the ground. I still don't know what causes that.
Another fun thing was what sounded like a kitchen knife as we were taxiing... I think it was actually the pilots testing the flaps.

I was a kid back then so I didn't know any better.
