My 98 GS 300 is clukning also. I experience it when comming off of higher speeds and usually after several miles of Driveing. I couldn't pin point it for a while and I too thought it had to do with the suspension,Bushings, Bearings,ETC... in the rear. Until finally I caght the exhuast viberating after I had parked and car. It was idleing rough and made the exhaust rattle and clunk. I still have'nt figured it out because it does'nt always clunk or rattle. If anyone out there has any tips please help... Because it's really annoying...