My AO Smith Promax water heater squeaks loudly

by Suzanne
(Chicago)

My AO Smith promax 75 gallon water heater was installed 5.5 years ago. I learned to live with the loud noise upon heating. However a few months ago it started squeaking very loudly upon heating, only for about a minute. I can hear this noise loudly throughout my house. I've been told I should just live with this noise and that my unit is old. I don't believe either is true. Does anyone have any suggestions? Unfortunately the problem began just a month or two beyond warranty.