I have an auto-fill valve in my in-ground pool. The pool is 9 years old. Recently I'm hearing a loud high pitch sound seemingly from the water source going into to auto-fill valve at the pool. I've not heard this in the previous 8+ years I've owned the pool. We've changed the float a couple of times, but to no avail. I believe the problem is the valve that the water flows thru at the water source, but can't seem to find a solution.