Noisy rearend 69 barracuda 318 car

Hey all
I just finished up a 69 barracuda convertible that hasn't been on the road sense 1991 so the first test drive i noticed that the rear end is noisy i think it is either a 7 1/4 or 8 1/4 not sure but defiantly not a 8 3/4 so the back plate comes off if you have the work on it. Like i said it was sitting outside for over 20 years and when i picked it up one the threat wheels was frozen to the brake shoes. So today i drained the fluid out of the pumpkin and put some MOPAR 90 weight lube in there to replace the nasty stuff that came out. My question is is there any additive i can add to help quiet it down? The car only has 60 thousand original miles on it so i think it might just need some drive time to help it out. Any suggestions would be deeply appreciated
Pat Faley
67 NB S Clone
69 Barracuda convertible
East Peoria IL