I just bought a condo (I'm a first-time homebuyer), and I've noticed a thumping noise coming from my bedroom ceiling whenever the (gas) hot water heater turns on. The noise starts within a couple minutes of the hot water heater coming on, and lasts for 15-30 minutes or so, decreasing in intensity and frequency over time.

This is brand-new construction, and the contractors are still on site, so I spoke with the site manager about this. He went up and listened to the noise, and said the noise was caused by the exhaust pipe from the hot water heater expanding and contracting, and knocking against wood as it does so. He said that the wood would eventually distort to conform to the pipe's expansion and contraction, but that I would continue to hear the noise until then.

Does this sound right? It seems strange that brand-new construction would have a problem like this: shouldn't they have built in enough clearance so that the pipe wouldn't be hitting wood? Forgive me if this is a silly question, but like I said, I'm a first-time homebuyer and this is all pretty new to me.