Slamming noise from passenger rear corner
 

I have a '81 300TD wagon. I replaced the air cells/ nitrogen cells/ hydraulic thingies and the front shocks during the summer with an immediate improvement in handling. Last time I checked, it appears that the SLS is working just fine.

Also the sway bar links in the rear were worn and replaced.

Still, I have this MASSIVE THUD from the rear passenger's corner with even the smallest bumps.

I checked to make sure that the jack and tool kit are secure and not rattling around.

Is it time for new rear shocks or is there something else I'm overlooking?