High-pitching beeping noise from trunk.
 

Strange problem that my dealer couldn't figure out.

If I lock the car by turning the key twice to the right there's a really high pitched sound coming from the trunk. I can also duplicate it sometimes by just holding the alarm remote near the trunk. Any ideas? Thanks!

Is there somebody in there?

Is it on when u hear this noise If it is then its probabaly ur fuel pump going out.

I would check your central locking pump. It should be behind the right side rear most panel in your trunck. I believe your locks are vacuum actuated. This is what creates the vacuum.