If the valve is still leaking, the water level in the tank would rise until it was going down the overflow tube. Probably not happening.
Note, sounds can travel quite a ways in pipes, so the issue may not be in your unit.
I'd go buy a water pressure gauge ($10-15 or so), get one with a second, tattle-tale, peak reading hand, then hook it up (maybe a washing machine supply, or the WH drain (careful, it can get hot), or if you have a hose bib, or nearly any faucet if you buy an adapter. Leave it on for 24-hours or so. Note the 'normal' pressure and the peak pressure. If either one gets above 80psi, then you need to address that, and that may resolve the problem. May not, but anything above 80psi should be addressed, regardless.