Noisey Hot Water Flow

IF you have a check valve at both the intake and exhaust for the water, that is the problem. Depending on how your system is installed will determine which check valve to remove. Usually, the intake(bottom check valve) is there because of the type winterizing system the OEM installed. There is no real reason to have the top check valve installed. If you remove the top, the noise will probably go away. What your problem is, with 2 check valves that is a restriction on both ends and causing that noise. Some Plumbing codes(not RVIA codes) dictate that there be a check valve on both the In and OUT of the water heater. Years ago, this was a problem on RV's built in California, as California had a state plumbing code that dictated both check valves and RV's had that noise problem. Once California modified the plumbing code to only require 1 check valve, that noise went away. Since the RV's we sold were not in California, we removed the Out Check valve to remove the noise. Doug