You said that you lost fuel pressure after a time. There is a fuel pres regulator in the cool fuel as well as up top of engine. The rubber internal diaphragm could be leaking fuel back to the tank.
Please do this to trouble shoot. With a volt meter .put ground lead onto the neg post of the battery that operates the fuel gauge with the problem. Place the positive lead onto the tank. Have some one start that engine. If positive voltage is found on the volt meter
there is a positive 12volt...
I think the noise you hear at idle is the engine trying to catching up with the transmission. To test is to raise the idle 50 rpm and the noise will go away. Mine does that too. Many threads on this at the Cruisers Yachts forum