As to the whistling sound, find a piece of small hose or tubing, small enough that you can stick one end up close to your ear, and long enough to probe the area in question with the other end. This makes it very easy to pinpoint the source of any suspect noise.
Another method I learned from my grandfather is to use a piece of broomhandle to pinpoint ticking/knocking sounds from inside the engine. Put one end against your skull above one ear, and place the other then against a part of the engine to be tested. You can easily "hear" what's going on inside the block or valve cover this way, and accurately locate and isolate noises this way.