We're definitely going for a (gas fired) instant heater once our existing (gas fired) tank dies.

But one unknown for us, is how much noise do these things produce when operating? Anyone know?

Our main motivation for going tankless is that our current tank unit is in a very suboptimal location, a good 15' from the nearest hot water outlet tap. Which means lots of wasted water as we wait for the warm stuff to arrive.

There's a much better location to put the heater, within 5' or so of all but one (the laundry) hot water tap here, but that new location is too small/cramped for a full tank.

Thus the real motivation for tankless in this situation, though the energy (and planet) savings are also a strong consideration.

Cheers