Hi David Ghislain, if he indeed services water heaters routinely, will know far more about this than I and I would defer to him for noises coming from inside your WH. However, your remark about sounding like a tea kettle would bother me just a tinsy-winsy bit.
The T/P (temperature/pressure) valve on the top or side of your water heater is designed to open when the water temp gets too high or the water pressure gets too high, or both. Check the pipe coming from this T/P valve to make sure there is no water coming out. If there is, I'd look at your water temp setting....could be a bit high.