After my neighbor's HVAC guy said our heater sounded like it was getting too much gas, I called the gas guy that did the install to come over and check it. I left him the installation manual for the heater. He said the pressure should be 3.5, whatever that means. Anyhow, he came by while I was at work and the heater still sounds loud. When I say loud, it can be heard from within my house. It is a constant low rumbling that can be heard while near the wall it is outside of. It is louder than our pump. I called the PB and he said it could have something to do with the water flow. Can anyone give an idea of how loud it should be and if gas flow is the only potential problem.