Dan is correct, they should be changed as a set as they wear as a set. Even if you just clean and repack your most likley going to mess up the seals. Take your time setting the new seals in place, clean the lip on the hub real well to remove any lip from rust or 30 plus years of road grime. They do make a seal setting tool that may be worth picking up, I have a set and they worth the price of no cursing seal install....

I've had my share of noises on my old bear..my latest is a clicking noise on the left front..turns out my trim ring I got from Carlisle this year is the culprit..anyhow as far as your bearings go it really is a good idea to at least pack them once a year..its probably the easiest thing to do next to an oil change on these cars and the explode factor is greatly reduced if done..if you find the bearing race or bearing rollers themselves to be scored or discolored at all then find a set of timkens and be done with it..its fun too..I still pack bearings by hand..I use Mobil one synthetic axle grease..I know I'm a minority here but I don't replace the oil seal..I can pop them out from the top side by smacking the inner wheel bearing with a brass punch and the seal pops out with no damage..I would rather keep a quality beat up GM part than replace it with something from China!! Good luck on the noises!! Hope its nothing major.