There is a big spring in that channel with the cables attached to each end, The cables run over phenolic pulleys at the
ends of the channel.
If one end comes loose you lose spring tension. I nearly lost 4 fingers last night when my center bay door lost a cable
and it slammed down really fast. It takes some grunt work to pull the cables back out and you just about have to be inside the bay
with the door closed to stretch them back into the eyes and pin them. Been there done that.
The drawbar on mine was rusted out and broke off the back of the bay door and I found a used one and had to fight with getting that back on and the fight with getting enough cable stretched out to reattach to the drawbar eyes.
The rattling sound is the spring laying in the bottom of its captive channel in all possibilities. I wish I could tell you how to actually
get the cables extended but I didn't think about it, I just did it. ( I clamped the cables with vice grips after attaching one end to the drawbar and then just kept pulling and clamping the other in place until I had enough to put the pin back in the eyelet.
Now I get to do it again....
If I get to that this week I will take pictures to show how I do it and make them available if you would like.
( keep in mind that I don't always do things like others do.. I can be original and creative sometimes and just
plain scary the rest of the time.