I searched through the archives without much luck other than the usual suspects that may fail -- rear wheel bearing or u-joint.

1990 Volvo 240 DL Wagon or Estate, M47 II transmission. 178,xxx miles or more.

Not that I drive the wee red beastie too much until the last month, with a new round trip daily commute of 54 miles at the speed limit, the:
- Rear suspension produces a growl a low rumble, at 36-38 MPH per the speedo, in a straight line, un acceleration or overrun (coasting) with clutch engaged or not, with clutch engaged and in forth or fifth gear.
- The rear suspension produces no growl, or rumble, at any speed, when starting out on the might I-90; when all is cool.

We have:
- New API GL-5 75-90W or round about mineral oil (as the owner manual recommends).
- Dropped the driveshaft, pulled the set screws on the rear two U-joints, and jacks it up with fresh new grease in the last few thousand miles. A good matching grease for the correct type recommended grease (forgotten what that is).
- New carrier bearing and newer bushing.
- Splined shaft well lubed up with NLGI-2

Wheel are sorely unbalanced, and I do plan to get these rebalanced before the ice age sets in or the we have a complete planet shutdown to pay off buttermilk bill. I had to purchase used tires and the used tire store used the half-speed power wheel balancer. These balance the wheel-tire assembly at like 35-50 mph. Not the best!

I think it may be the one or both U-joints, wheel bearings, or ??? Even though it all should be lubed up correctly.

cheers and thanks,

Buttermilk MacDuff.
--
Rumbly Volvo 240 rear axle.