The front-end rattle is probably the same one lots of other GM owners are experiencing - a problem with the intermediate steering shaft is about one-eighth of inch in diameter too small. GM dealers have been packing the shaft housing with lube (gease), as per GM's instructions on the remedy. Of course this doesn't last too long; replacing the shaft with one that actually fits into a bearing or bushing without any play is really the only way to solve the problem.
Has anyone managed to get GM to install the revised-design intermediate steering shaft ?