it was SO LOUD and so consistent. very scary.
to answer your question about roofs, YES, putting a layer of shingles over the old shingles is a standard practice. One can only put 2, maybe 3 layers on without putting undue weight on the roof, tho and it's not necessarily a 'fix' for leaks.
I have to say, taking care of your roof is essential to keeping the house intact. Water goes EVERYWHERE and causes damage we can't always see. It's why hubby and I spent the money on a metal roof with a 100 year transferrable warranty. I don't want to worry about a roof again, I already did that. LOL.
But the BEST way to replace a roof is to have the old shingles removed, the plywood inspected and replaced if needed, a new waterproof membrane and shingles.