I have an 01 X5 4.4 with 90,000 miles which has started making a really annoying noise.

When I am idling in drive with my foot on the brake pedal, there is an embarrasing rattling noise coming from what sounds like somewhere in the engine compartment.

If I put it into neutral or park while keeping my foot on the brake, the noise goes away.

Any ideas on how to fix this?