I know they make a dye that you can add to fluids that shows up under a black light, great for finding leaks. It sounds like the oil may not be getting where it need to in the top end of the engine. I don't go around feeling how soon the oil filter heats up, so I cant tell you if thats normal or not. I would have the pressure tested and see if its in spec or not. Of course you could also try just replacing the filter and adding oil to make up any difference.
Try getting some hose, and sticking one end in your ear and use the other to try and pinpoint where the noise is coming from.
