somthing vibrating/rattling in the engine compartment

[auto pal]

have any of you guys heard or felt like there's something
vibrating/rattling in the engine compartment, somewhere in front
of the steering wheel (left-hand drive), when the engine is idling
or when it's in drive or reverse and you're stepping on the brakes?

yesterday, i found out that it's the air filter box vibrating. there
must be something loose with the mounting or something because
when i press or put pressure on the box the vibrating stops.

haven't worked on it yet, though. maybe, this weekend.