i have a p reg 1.8 vectra as well. It does exactly the same thing and has been to the garage. When the 5th gear jumps out, you can sometimes prevent it from doing so again by moving into 5th gear again and keep your hand firmly pushing on the gear stick (in 5th) untill after you have brought up the clutch, then let go of the gear stick. This stops it jumping out striaght away again. The problem is due to general wear of the gear box which tends to happen to these cars and can only be completly solved with a new gear box, which isn't always necessary. As for the rattleing, i'm not sure, but my car does it too.
Becca, May 2006
