Standard Air Intake - Top Cover??

[Juliand]

Only had my car a few months, but today noticed something looking to be missing from the standard air intake (to right of engine cover, above fan). Puzzled, I had a look around the bottom of the engine bay, and spotted the small oblong top cover, just loose, but slightly wedged by the fan. Should there be anything else inside this housing?

I've put this cover back on, but just hope that it has not damaged the fan in any way - how can I check, please (sitting in stationary with engine running until it kicks in, perhaps?). I have noticed  a loudish whirring a couple of times in the last week, but just put it down to using the AC more, in the heat.

It may have been off since I bought the car, perhaps knocked off when the dealer cleaned  the engine bay - I dunno!

Any thoughts / comments / suggestions  welcome.
Thanks

[Dan_FR]

They have a habit of escaping during motorway driving as the air passing through builds pressure. Lost mine on route to R-Tech a few years back.

You should be able to visually inspect the fans (turn blades by hand). Any damage would be very obvious as soon as they started as the imbalance would cause lots of noise and vibration.