We live in a single story house about 5 years old. It is in Vegas so we have no basement or crawl space just a slab of cement. Lately when we flush one of the toilets we here a load vibrating noise (for about 3 seconds) from the attic and wall after the toilet has filled.
This happens after each flush but only if the toilet hasn't been used in the past 30 minutes or so. If you flush it again within a 30 min span the noise is either lessened or gone all together.