MY hot water heater is making a low whistling noise. IT stops when I shut power off to heater. No water is coming from valve, I have tried the value aprx 8 times times and when I do water does come out of it so it does not seem to be stuck.

That valve is a temmperature and pressure release valve. If the noise is coming from there and there is no water coming out it is probably because of excess temperature. Bet you water is really hot. Sounds like you need a new thernostat. Is that gas or electric, what is the temperature setting.

It is electric, the temperature was 135/125 have since then lowered to 130/120... not making noise since readjusted temp

Every time you open and close the T&P you increase the chances that it will not seal completely. Stop trying the valve, it's a safety valve that can get debris caught in the seal, that happens you must replace it. Let us know if the whistle comes back.

I agree with Bob that the whistle will probably come back. I believe the T&P valve is set to release at about 170. You should check the actual temperature of the water with a thermostat.

I have tested the water numerous times under different scenarios, the temperature never goes above 130, I have the settings at 130/120. We noticed to day the sounds is not as much as whistle but the sounds of water when gets hot, there is no steam/water coming from pressure release valve and the sound sis not as noticeable. I just drained the tank and cleaned the elements aprox 2 months ago and we do not have hard water.

Draining the tank is not flushing the tank. To flush you leave your main turned on and use the city pressure to blow the debris out of the heater.

One other thing to check. Do you have a check valve on the cold water line. If you have a sprinkler system you will have one. When the water is heated it expands. If you do not have a check valve on the cold water line the pressure moves back up the cold water line. If you have a check valve it cannot and pressure builds up in the tank. If you have a check valve for what ever reason, you have to install an expansion tank on the water heater. Just one more thing to check.

No Check Valve On Cold Water Line