Whenever I start the engine in my Expy 5.4 for the first time each day, I notice a brief sound similar to a donut gasket leaking sound, or exhaust manifold leak. This only last for about 2 seconds then it goes away. Any ideas? I've listened to the engine running and haven't heard any unusual noises.

 

>>>>Mine truck has the 5.4 and it would do that. At first it would go away after the motor got warm. Then it continued on even after the engine was at operating temp, though it wouldn't be as loud. I was still under warranty and took it to the dealer. It ended up being a broken stud on the right side manifold. For what it's worth, could be your problem.

P.S. Had a crown victoria at work that had the exact same problem with a 4.6 with broken manifold studs. I've seen a few crown victorias have that problem.