I think someone asked about he mesh stuff before and the answer was this.
The mesh is used only to protect the underlaying bellows. This bellows, which looks like an acordian is made of one piece of metal so it can should not leak.
the sound you hear could be commng from a number of sources.
like mentioned before, with the wheels chocked, transmission in neutral or park, and the emergency brake set have an assistant hold the engine at the RPM where the sound is heard while you inspect for its source.
