Annoying rattle when starting

[paneuro]

I have a 2008 530D E61 and have a metallic rattle whenever the engine starts, it only does it once when the engine starts. I have had my son start and stop the car several times and it sounds like it is coming from the front of the engine. I have recently replaced the serpentine belt as it failed and ended up in shreds and I had to cut it off. I'm wondering if it could be something to do with the idler pulley. Has anybody had a problem like this before. thanks Paneuro.

[Greydog]

Hi Andrew

If you have had a shredded belt I would check the whole system belts don't just shred 

Main suspect for me would be start with the Crank shaft damper pulley they can detach from the rubber insert and wobble causes the AC belt and Serpentine belt to rub on each other and fray. I would also check all Idler and Tension pulleys plus while things are loose the waterpump,Alternator and AC compressor 

Dave