Insinkerator has stainless steel tank but does not have anode rod to protect against depleted tank wall.Leaking tank means broken weld, and you must replace tank.Copy following link for tips installing under counter heaterhttp://waterheatertimer.org/How-to-install-under-counter-water-heater.htmlAdd comment as needed and fixya will send me email to reply with more detail as needed If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7
I had also this problem before, same with buzzing sounds on my Amtrol Boilermate and all I had to do was to call the local dealer and they have got it fixed.