What kind of pressure regulator do you have? The inexpensive regulators are really restrictors and after a short time the pressure on both sides will equalize. Then when you use higher volumes of water, the flow will appear restricted. You need to get a true regulator usually about $60-$80 (ieValterra A01-1117VP Brass Lead-Free Adjustable Water Regulator)
These will hold the set pressure regardless of flow. Occasional drips from the over pressure relief valve is possible due to the expansion of the heated water and the lack of sufficient air space in the top of the WH. With regard to the noise from the WH when running hot water, I assume you are running it on 110VAC. What you are hearing is the heating element heating up and heating the water around it. This is perfectly normal.
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