Do they just do it when they are cold? When I first leave out after the trailer has been parked overnite, mine are very sticky and grabby, making a groaning sound. After traveling a few miles, they quiet down and act normally. (1979 28' Ambassador trailer, similar vintage and length to yours) When I regreased the bearings this spring, the pads had plenty of life left, so they are not worn out. I also get a bit of groaning from the friction anti-sway bar on the hitch.
T.V.:'05 Dodge Ram 2500 4x4 Quad Cab Cummins