Most tankless water heaters are louder than you expect if you never used one. So making noise is good thing.
In ours the noise is somewhere between the sound of the water pump and the propane heater burner (before the fan comes on).
If water is not flowing, or the burner does not ignite (no propane), the unit will not function. So sounds like you have the bypass valves set correctly and water is going through the on demand.
Scott and Liz - Southern NM
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