For the record, I am a plumbing contractor in the East S.F. Bay Area of northern California; 30+ years experience.
I am wondering if anyone has experience with the new stainless steel tank Insinkerator HC1100? They have retired the original design and gone with a stainless steel tank for longer warranty and service life.
I found the first new tank to make excessive noise while heating, like a jet taking off, so they sent a second. I got the second free replacement installed a few weeks ago.
The issue is that the tank really rumbles loudly when maintaining tank temp., which lasts a little more than one minute.
The people I have spoken with at ISE, so far, think it is the new 'normal', but I have not got any other installations to compare it with.
My experience with Franke and Kitchen Aid are that they are pretty quiet, as was the original leak prone copper tank ISE.