I'm sorry to hear that your CEL is back. Unfortunately, if the rattling sound is concurrent with the engine light, then the problem is not as simple as a broken exhaust hangers. A bad catalytic converter could set a code (sometimes they do, sometimes they don't) and will probably cost between $200 & $400 to replace.

The other thing it could be is engine knock. I'm not personally familiar with the sounds made by an engine knocking, but from what I've read it might sound like what you're describing. Are you running premium fuel? If not, you need to.

 

i'm using 95. the manual recommends 98 for sporty drive and 95 for normal drive.

i will change to 98 as soon as the gas tank is empty.
i'm taking it to the mechanic in the morning. most likely the catalytic converter and another 400€ spent..

why does a catalytic converter go bad anyway? is it because of gas? or maybe it's just the 140 000 KM on it?

 

Usually the catalytic converters don't go bad. When they do, it's often caused by some other engine malfunction, or physical damage. I've got 130K miles (209K kilometers) on mine and no problems.