I have a rattle coming from my engine (545i) when the car is idling. Under load of any kind (if i touch the gas peddle), it dissapears. Almost sounds like an idler pulley bearing is shot or something but doesn't seem to make sense that it dissapears under load.

Similar sound to this (both the rattle and the pulsing)
https://www.youtube.com/watch?v=yEkn...ature=youtu.be

Any quick ideas before i dive into it?

 

My idler pulley (or deflection pulley) below the alternator made more of a screeching noise at idle and would disappear under load. I sprayed it with lubrication and the noise is no longer an issue.

The rattling noise could be from your water pump. How many miles on your 545? Mine went out at ~60k, and it's been known to frequently fail at a relatively early stage. With that said however, a failed water pump will usually get louder under load. Get a mechanics stethoscope and place it on the water pump. Good luck.