I hope someone is able to provide some guidance.

Yesterday, I installed a new water heater. It's a Richmond (from ******* made by Rheem) 50 gallon gas water heater. After firing it up for the first time, there is an irregular resonance heard from the flue. I disconnected for a few seconds the flue so that the heater vented directly into the basement and the resonance was still there. If you cover the opening to the flue where it comes out of the heater, the noise completely stops.

When the heater is making the noise, you can hear it also around the bottom of the tank where the burner is located.

I tried rotating the baffle to see if the helped (it did not) and tried lifting the baffle out while it was making the noise. There was no discernable change in pitch to the resonance.

It seems to just be more annoying than anything else. But, you can hear it faintly upstairs on the first floor and I think over time will get on my last nerve.

Any thoughts?