Nuisance or danger - banging pipes

Hi - we recently had our townhouse totally re-plumbed with CPVC supply pipes (to replace the defective polybutylene it was built with). About 7 months later some of the pipes have started to make a banging noise after the water is shut off on certain faucets. The noise is not too loud (more like a tap, tap, tap) and only lasts about 30 seconds after the water is shut off.

My question: Is this likely to cause an eventual catastrophic pipe breakage? Or even a non-catastrophic one?
The plumber warrantied the project for a year. But I dunno if he's gonna cover replacing the drywall that will have to be cut into to secure the pipes (if that's what the problem is).
Thanks,
Donk

Up to 30 seconds afterwards?
Sound like expansion and contraction of the pipe rubbing against wood or clips as it warms and then cools.
Sort of a Tick, Tick, Tick, ?

I wouldn't worry about it.