Boxster Wiggle

[Pastor T]

Ok guys, here is one for you guys. My 2000 Boxster 2.7, 185,000 miles, has a tracking issue in the rear. When going down the road in a straight line 50 mph and above, the rear end darts back-and-forth almost like you were driving on some kind of grooved pavement.  it’s not like the car is fishtailing, it’s just a wiggle.  i’ve had the car up on Jack’s and been all over underneath. I see nothing loose or out of place. I’ve pushed and pulled and tugged on everything. I’ve checked every nut and bolt on all of the suspension sway bars, etc., nothing loose. Wheel bearings are good, shock mounts are good. I’ve had it on jackstands with the rear tires hanging free i.e. no weight. I’ve had it on jackstands and then jacked up each tire so that it is holding weight and checked it for anything loose.  I changed my tires, Michelin pilot sport, and put my sticky track tires on. It still does the same thing.  the only thing that I can figure is it may be the steering rack. I don’t feel any play in the wheel. I don’t feel any play while driving and the rear end is wiggling. Recently change the front motor mount  so that is good. I have never changed the two transmission mounts. This has got me stumped. I’ve owned the car for 13 years and put 100,000 miles on it. I’ve never seen or felt anything like it. has anybody got any  bona fide ideas. Please, no jokes, I’m way past that. thanks in advance.