Front End Plonk

[Laz]

I've gathered opinions (all reasonable) that the noise could be the sway bar drop links (retorque or replace -- they were replaced and torqued properly,) upper strut bushings/bearings/plates, lower control arms (whole assembly only, no replaceable bushings,) radiators (the noise is heat-dependent; only occurs after car is fully warmed.)

Checked/damped/removed as many trunk panels as possible, checked and shimmed underbody/wheelwell panels, checked under dashboard/removed one passenger side cover panel, removed headlamp units. Damped the trunk lid and latch mechanism.

Went to a good local shop today, which fortunately has a street nearby that allows the noise to occur, and had them use their "electronic ear" to check the upper strut by attaching the sensors to the mounting bolts inside the trunk, and also to a lower control arm near the hub carrier (on the side that seems to be making the most noise.) No conclusive results. Two Porsche dealers haven't been able to find the cause, and a couple years ago when the rear had the same noise, a third dealer changed out a lot of the rear suspension which solved the problem, but they couldn't say what the actual cause was either.

When I got home, I placed one end of a short strip of oak against various suspension pieces and rapped the other end sharply with the palm of my hand. When I rapped it against the front springs, I got a noise that sounded a lot like the plonk. I compared the noise against the rears', and those seemed well "seated" as the sound was a solid thunk with some slight ringing. I found that I could even just pluck and poke the fronts with stiffened fingers and get a hollow rattling, which began to diminish as the car cooled down. Near as I could tell, the rattle seemed to be coming from the bottom of the springs where they seat against the struts.

I think I'm finally on to something, and tomorrow will go back to the shop to demonstrate my method. QUESTION: are there replacable shims or somesuch between the spring bottoms and the struts? (I'm aware of the bushings and plastic(?) plates at the tops.)

Thanks for your patience and consideration: I know this has been a long post.