I do not have the sport suspension.... the car is driven conscientiously avoiding potholes, etc. & I keep it aligned, tire pressures right, etc. I had the ball joint/lower arms replaced all the way around about a year ago. Recently I have noticed an intermittent "knocking" or "clunking" sound from the right side, almost like something was loose in the trunk. I just had my indy thoroughly inspect the suspension, springs and shocks, dreading another major expense since I recently forked out 1700. for new Xenon assemblies. A nice surprise: bushings and joints all around are generally tight, not needing replacement. The shocks have life left in them/ not leaking or oozing, and bump stomps are also good, so they are OK for now. And the springs are good. Phew! What could this weird, occasionally bothersome sound be eminating from? Well, my indy said don't worry about it.... the car is "sound"... Just for $hits and giggles, I gave the underbody a dose of Griot's Gargae Undercarriage Spray, and hit the bushings, links and joints. Let it sit overnight. Drove the fam around the next morning, and it was quieter. So I gave it another dose, and it is altogether absent of the noise now. That did it! No more clunking... the car is quiet even on the cobblestone of Zionsville Village-- the acid test. Isn't it funny how the days of oil change and "lube" are gone.... the "lube" part anyway--- where they would grease up the supsension joints. That's in effect what I did, kinda, and it quieted things down... we'll see how long it lasts. Just thought you 'e39ers' would like to know....
I had a creaking or rattling simular to what your discribing. I found my swaybar links were worn and the noises stopped after there replacement. It is a very simple job at least on a 95 540i. Hope it helps.
Given what worked for you, my guess would be a dry bushing that was not clunking so much as sticking and then suddenly shifting in its bore. Lubrication would fix that - for awhile.
My 2002 530i had about 80k miles when I worked on my suspension this summer. The two symptoms I had were a shuttering in the front during aggressive turns and occasional squeaks in the rear. I set out to replace the shocks, install firmer springs, and upgrade the sway bars. I opted for Bilstein Sport struts, H&R Sport springs, and an Eibach anti-roll kit. The results were amazing. More on that in a moment. While doing this work I discovered some problem areas. The rear sway bar links were a little loose. These were inexpensive and easy to replace. However, I also found out that the rubber seals around the ball joints in the lower control arm bushings were split--on both sides of the car! The ball joints cannot be replaced by themselves. You need to replace the control arms. Again, it was relatively inexpensive and easy. I also replaced the front sway bar links while I was in there. I believe that the tired Sach shocks were the problem with the front end shuttering. It could have been the rear sway bar links, the control arm joints, or sway bar bushings, causing the squeaks. While I floated and shuttered in the Advanced Driving School at NHMS class in the spring, the car was downright "snappy" when I took the class again in the fall. Instead of shuttering, I hear a groan but do not feel any shutter when going into an over steer condition. The sound is consistent and provides great feedback. When I quickly unwind the steering until the groan just disappears, the front is gripping again. If I relied solely on seat-of-the-pants feedback, I would overcompensate with the steering. A few more HP and I could be drifting with a grocery getter... Note: You need to drop the front suspension sub frame in order to install a front sway bar. I farmed this job out to a local mechanic who services BMW's.
