Where's the pump in this picture? and what kind is it?

The pump is not separate; it is built in to the Rinnai unit.

We don't know how loud it is or what it sounds like - we can't tell you if it's normal.

Also, if the pump is on the burner is on also. you would have to determine if it's the pump or the burner / fan.

When the pump has run and then turned off, have someone else run hot water. This should kick on the burner and not the pump. See if the sound is the same.

Jake, thank you for suggesting that we determine whether the noise is the same whether or not the burner is on. It is not. The noise occurs only when the burner is off and the pump is on. We know this because the controller (see pic below) indicates burner status via a flame icon to the left of the temperature. When the burner is on, the flame icon shows. At the same time, a red light on the tankless unit flashes slowly. According to the manual, this "indicates ignition and pump operation." The annoying noise does not occur during this time. It happens right after the the flame icon disappears and the red light goes into rapid flash, which "indicates pump operation with no ignition." The noise stops when the flame icon reappears and the red light goes back to slow flashes. Your post seemed to suggest that the fan (which our plumber suggested was the source of the noise) is connected to the burner operation, not the pump. From the info I've given you now, do you have further advice or comments? Or does anyone else? Thank you very much.

Jake, many thanks. Knowing nothing about plumbing or mechanics, my previous Google searches weren't specific enough to bring helpful results. But now by Googling "bad Rinnai tankless fan" (fan being the key word I hadn't included before) I immediately found several plumbing forums where this exact problem was dissected at length. I now feel confident that the answer to my question (is this noise normal?) is no, it's not. So I will call the installing plumbers to come check the fan and whatever else may be causing this situation. I'll report back here if and when we get a solution. Thank you again and have a wonderful day.

Did the plumber figure out the issue? I just turned on the circ function and was surprised how loud it is. Wondering if it's normal or if mine has an issue too.

Funny you should ask now, rsekman, because the plumbers were just here this week. The short answer is no, it hasn't been figured out. Last spring after I wrote those posts, the plumbers came back, checked everything, and found the Rinnai unit door to be a little loose. So they tightened it and that did help with the noise - a bit. We also are having water temp issues (for example, unit is set to 120 degrees, but "hot" water is more like 108 max at some faucets, even with recirc. And one faucet puts out warm water when set to cold. Not great for washing lettuce.) So the noise issue went on the back burner while they tried to solve temp problems. Meanwhile, as snowbirds, it was time for us to go back up north, so six months went by until we returned to this house recently. When they came back this week, they said, "Whoa, we've never heard a unit that loud! It should sound like a hair dryer on low; nothing more." To which I replied, "So we're not crazy!" They think it's the internal fan. They also decided the unit may be defective and so now they're in the process of contacting Rinnai about it. It's pretty discouraging to spend thousands of dollars on something you think is going to be a great improvement over your previous system and a year later, you're still having issues. Good luck! Please post here if you get any answers and I will do the same.

I'm so sorry to hear that. What has me confused is that it didn't start until i turned on the circulation feature. I guess if it continues I'll have to turn it off and wait for the water to warm up. Still not sure about the cost of wasting cold water versus running the gas more in recirc mode. Please do keep us posted if you find out more. I'm still trying to find out exactly what is making the noise. By the time I run down to it after hearing it, it has stopped.

Is yours a new unit? Or have you had it for some time with no noise problems and now suddenly it's loud when recirc goes on?

Re your comment, "Still not sure about the cost of wasting cold water versus running the gas more in recirc mode" - I'm still confused about that, too.

I’m having this same issue. Unit was newly installed yesterday.

RSC199 does this too. I will never buy Rinnai again. Navien all the way.