2002 300M with Performance Handling Package. 135K miles.

Not-so-loud low-pitched "clunking" noise on uneven surfaces at low speed
-- e.g., when coasting (not necessarily braking) as I approach a red
light or stop sign.

Can't say that I've noticed the noise at higher speeds.

No suspension or steering parts have ever been replaced.

Where do I start looking? What might it cost me to fix? What special
tools would I need to tackle the job myself?

Perce