Hot water tank noise

[Sacramento Dave]

My hot water tank has started making a odd noise, it's not the normal poppy sound from tank deposits. The best description would be a half second drum roil about every 10 seconds. ( almost like a animal scratching itself in the wall) I have drained the water out of the system thinking it might be some kind of air harmer, Drained some of the water out of tank, the only way I have got it to stop is to shut the water to tank off and blow some water out of PRV. The tank is about 7 years old 50Gal, GE, self cleaning. It's pretty much non stop so any suggestion would be a help. Thanks

[Joseph Meehan]

Do you have an anti-siphon valve? How about an expansion tank in your system? You may need one or you may need the one you have made functional again.

[Sacramento Dave]

they piped any air chambers in system) I do have to shock arrestors I am going to pipe the system. We have had the house about six months I am doing allot of remodel but plumbing wise have only changed some fixtures and replaced quiet a few angle stops, From the very small amount of plumbing that is exposed it looks like a kid did it not even close to code. (it's on a to do list) The noise has stopped why I don't know. But we do have a home warranty I might get a new water heater for a $45 dollar deductible.It is just a odd noise almost like a lose piece of metal rattling in the tank.