Hello,

I have a 900 series car but your symptoms were like mine last time. I was driving on the highway with family inside doing 100km/h smooth sailing then suddenly a loud rattling noise just like you've described came from underneath the car. It sounded like loose pebbles in a can.

Stopped the car by the roadside and shone a light underneath but couldn't see anything loose. I continued the journey driving slowly to my destination about 100km away with rattling all the while. The rattling changes with road speed. At lower road speed the sound decreased. Driving with free gear still don't eliminate the rattling. However at one time the noise just went away during the drive.

Next day I brought the car to my Volvo mechanics. It turned out to be the rubber support doughnut around the centre bearing had broken. In the end he replaced the doughnut with centre bearing too (as preventive maintenance). No more noise.

You can replace the doughnut only - it just slips onto the centre bearing. But to do that the entire driveshaft must be taken out. Be sure to mark the alignment between the two halves of the shaft so that they align the same during installation. Otherwise it may go out balance and vibrate during drive. In latter version of driveshaft (like mine) the alignment is keyed - only one way to install the two halves back.

Hope this helps.
Amarin.

check the U-joints.
when the car is stationary the u joints won't move very much unless they R very worn.
it doesn't take very much wear to have the joints move around more than they should normally-check the intermediate bearing and the boot
check the carrier mount on the transmission and from there also look at the extension on the transmission. if there is any leaking fluid the seal needs replacing and the sleeve bearing & possible the gasket between the small housing and the main trans. block. U-joints, bearings, seals, R not difficult to replace on your own, if you have the tools. Takes time tho.
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89-740 GLE;91-940 Sedan ;98-V90 Wagon ___ all running well