rear end? noise from my 300sd

[fj bertrand]

Hello all. On my 85 300sd with 262k. When turning left, I hear speed dependant (speeds up or slows down on road speed). squeal, like brakes rubbing. I drive along a left turn bridge, hear the sound realwell as it bounces off the bridge barricades. I hit the brakes the sound continues, I apply the parking brake and the noise is still there. Drive straight,or a right turn, no noise. I am figuring that it is the differential as it would work on a turn, and something is bad. I thought it might be the axle drive shafts, but they are tight on both sides with good rubber boots. No leaks, no shiny spots where a tire might rub. So I am just about positive its the pumpkin ball. Any thoughts??