Yesterday, my 2000 s40 developed a pronounced shake, and a clacking sound that speeds up with speed. At a slow speed it feels almost like a bent rim, but then around 60 mph its a quick shimmy. It sounds like its on the driver side. It started yesterday, then it disappeared for awhile at high speed (70+) and it didn't do it today until midway through my commute. I revved it in nuetral and the engine is running smooth, so its probably something in the driveline. It seemed almost like the wheel lugs were loose. I'll check that, but its probably not that. Any ideas???????????

 

Maybe bad Axle.
I have also seen the Transmissions break as well and cause the same thing.

 

could be a balance issue with ur tires, when was the last time u had them rotated or changed?

 

I had the same problem. Dealer had to replace the front axle.