Help with diagnosis

[Cajundaddy]

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.

[Dale_K]

When you say you changed the wheels do you mean you drove the car on a different set of wheels with different tires? My first thought would be a tire with internal damage and I can't tell if you ruled that out. Does it do it in every gear?

[dad911]

I would have mechanic carefully put the car on the lift, raise it a few feet, run the car. You should be able to pinpoint the sound.

With 97k miles my money would be on the cv joints, have they been changed recently?

[Cajundaddy]

Thanks for the input guys.
Yes I have 3 sets of wheels/tires so my first step in the diagnosis was to swap wheels and see if it was just a tire delam problem... nope. The noise is present in every gear and increases with speed. Thorough checking of CV joints, axle bolts are next before considering a fresh trans. Getting the car up in the air and running it through the gears is a good idea.

[Cajundaddy]

Update, definitely internal trans bearing noise. Replacement trans is in route. While we are in there a fresh clutch, flywheel, RMS, IMS bearing, are getting done.

FYI: The original IMS came our today and it was in very good condition. It was clearly not new but both seals were still intact and there was no noticeable bearing play. Not bad for 13 years and 97K miles.