our house is 25 yrs old plumping in good shape new press tank,press reg,faucets,shower heads,instant h2o heaters... problem is hot water whistles mostly in shower but now has moved to kitchen sink. we used 2 have an 80 gallon electric h20 tank it made the same noise. Anybody know how 2 get rid of the problem? When the whistle occurs, our water is nice and hot as it should be. When the whistle stops (5-10 mins later) the temperature drops considerably.