[jakeru]

If the clicking varies with vehicle speed, I'd first look into dry (torn boot allows grease loss) or worn cv joints, since they are common wear items (especially the rubber boots) at this age, and could certainly cause the symptom described. If not cv joints, I'd look at the final drive of the transmission, such as the ring and pinion, because I wouldn't know what else it could possibly be.*

* That is, assuming the clicking is proportional to vehicle speed. Suspension noise would be sensitive to road roughness or bumps and not necessarily vehicle speed. If you aren't sure what you're hearing, you could try recording it and posting it here, perhaps.

I've had multi-piece wheels making a clicking noise proportional to vehicle speed, but it wasn't torque sensitive. Plus, I don't believe you have multi-piece wheels. But for good measure, you might as well check your lug nuts for proper torque, if you haven't already. Good luck. Check out those cv boots closely!

Also, even if the boot isn't torn, it may still be possible that the previous owner could have done a sloppy/incomplete repair on a torn boot that allowed grease to escape, dirt to enter, and cv joint to wear. Simply replacing the boot in this case wouldn't have properly repaired the problem. You might be able to get a hint if the boot is origiginsl or not if you look at details like if it has original looking clamps. At your boxster's mileage, I actually would be surprised if it were on its original cv boots and they weren't torn.

My 2001 boxster base with 115k miles has inner cv boots that are just starting to crack, by the way. They aren't completely torn all the way around yet, but are in need of service soon. Outer cv joint boots are OK. Hope that helps; good luck!