Use a long screwdriver/pry bar/rod to pinpoint the noise. Place the tip of the screwdriver on a component (say the power steering pump) then carefully lean over and place your ear on the handle. You can use just about anything like a stethiscope just be very careful while the enging is running. Most parts store sell an actual automotive stethiscope for a couple bucks. You'll be amazed the noises you can hear inside the engine (start on the valve cover then work your way down the side to the engine block). In any case, when you find the howling noise, make sure to move the listening point around that general area to pinpoint where it is loudest.

Another thing you can try is to temporarily remove all of the belts then start the engine (do this when it's cold and don't run it too long since the water pump is not spinning). If the howling stopped then you know it's one of the accessories. Put one belt back on and repeat to figure out which accessory is the culprit.

Good luck!