Help with diagnosis
 

Ok, my car recently developed a thumping sound that varies with speed (tire rotation) and not rpm. It started as a faint sound like tire pickup on the left rear. As I drove home it became more like a nail in the tire, then a lag bolt in the tire, now getting louder more mechanical sounding. I changed the wheels, inspected the brakes and rotors, inspected the CV joint boots and all looks a-ok. The wheel bearings are 6 months old. Preliminary diagnosis from my trusted Porsche mechanic is that the trans is going south.

What say you??

This is a 98 2.5L Boxster 5spd with 97K miles and 50+ track days. Trans fluid is changed annually with no obvious signs of serious problems. I have noticed that she has been stiffer shifting lately but attributed that to cables and bushings. I generally shift gently and have never had a synchro failure. I adjust my driving style so I rarely generate wheel spin on the track.

Have you ...
 

... checked the half axle flanges on the tranny?
I once had a customer with the same symptoms and one of the flange bolts was missing and three others were loose.
Happy Boxstering,
Pedro

Thanks for the input Pedro. I'll check that tomorrow.

does it do it with no power to the wheels...clutch in and coasting?

louder or softer when turning...loading or unloading the corners?

Yes, it doesn't matter if the clutch is in or out. It does get louder in a right turn when loading the left side wheels.

Topless; perhaps the left wheel bearing ??

Yes I have not ruled this out. All 4 wheel bearings were replaced 6 months ago and preliminary tests did not indicate a bad bearing. I couldn't get to my car this weekend cause the shop was closed but I will dig deeper Monday. Hoping it's NOT the trans :o