Sounds like another of those "modern" Harley dealerships, owned and run by a used car dealer. They should have offered to take a gas cap from a bike in inventory (doesn't have to be chrome or an exact match, it's just temporary) until they could get you the correct cap. They should have done this anyway, to verify their diagnosis of a defective cap. Now you are waiting for a cap with the bike sitting in their shop instead of in your possession, and you have no idea if a new cap will actually fix the problem. No way would I pay for shipping for a warranty part, and if they didn't want to loan you a gas cap until they could get one in I think I would have spoken to the actual dealer, not his flunkies, and suggested he either take care of the problem immediately or give me my money back. These places are run just like used car lots, once you sign on the dotted line you are nothing to them.
As for the noise problem, AJDR^ gave you the answer. Insist they bring out another similar bike and compare noise levels to your bike. The M8 engine is significantly quieter than the old Twin Cams, and it is not "normal" for them to make excessive noise. This is another sign of the lack of professionalism found in so many Harley shops these days. Know nothing and do nothing types, just like at those used car lots I mentioned before.
Jerry