[MrClean]

I recently biult a Heckler and used a XT 760A front derailleur. When in the middle chainring the "cage" rattles up a storm. If I tighten the High or Low limit screws the rattling stops, but I can't shift to the big or granny ring respectivly.

Any ideas how to get rid of the rattle?

 

[cort]

I recently biult a Heckler and used a XT 760A front derailleur. When in the middle chainring the "cage" rattles up a storm. If I tighten the High or Low limit screws the rattling stops, but I can't shift to the big or granny ring respectivly.

Any ideas how to get rid of the rattle?

If you can wiggle the mechanism a few mm's in both directions, its a good sign you need a new FD
(When it gets this bad the shifting becomes poor)

 

[rockyuphill]

In the middle ring the cable should be under substantial tension, so the derailleur mechanism shouldn't have any loose rattley bits at all. You want to confirm it's the cage rattling and not the chain on the cage. Tap it with a screwdriver handle to excite the rattle. If anything on the derailleur is really loose then something is likely broken.