ok i know you have checked that......can you lift the rear of the car and try to spin the rear wheels?Of course it would be better on the ground but i do not know your set up.I would do it like this .I `d lift the left rear and start the car shift 1-2-3- with the right wheel on the ground...it will only spin the left-but only if you do NOT have limited slip differential!!

Ivan

The fact that it seems to be rotational and increase when there’s braking - It sounds like some kind of movement when pressure is applied. I had a similar shake and clunk in my 124, it turned out to be that most of the bushings in the rear were shot and the rear was basically coming loose especially when braking.

It could be a CV, but I imagine if that was going then you would be hearing more of a click sound and it should be especially evident when turning.

Couple of other things to check. Check the sway bars, especially the rear, I had a clunk in the rear that ended up being a loose link, it sounded like that, but less rotational. Check the banana arm bushings, check torsion bar cover bolts, check and make sure the struts are torqued correctly.

When bearings go they are pretty damn loud, it should almost sound like a whoa whoa whoa whoa hum with maybe some screeching. Ask me how I know.

Only other thing I can think of is if the caliper itself has some kind of play in it and isn’t bolted down properly. And not for nothing but check and make sure the rear hub bolts are torqued properly.

Thanks to all for advice. After running it with the rears wheels off the ground and still hearing it, I gave up and checked it into the hospital.

I found absolutely nothing loose. Anywhere. Pulled pads and rotated, shook rotors, spun and listened. Put it back together, ran as noted above and decided it is a DIY checkbook project.

Hopefully answer soon.

I strongly dislike giving up but also dislike spending $$ to fix what I think it is only to find it is something else.

Porsche hospital called. They claim to have isolated the noise to a rear rotor. Their suggestion was to replace my vented, cross drilled Zimmermans with stock rotors at all 4 corners. They strongly dislike crossdrilled rotors for some reason but I am not willing to replace 4 rotors when I can get by with 2.
So... I ordered a new pair of Zimmermans from our host and will replace just the rears when they arrive. Nice morning project.

It could be possible that the backing plate is bent slightly and rubbing on the rotor.
I had this happen to me when I replaced the rotors on my Toyota Tundra. When I pulled the old rotor off, the emergency brake shoes were catching on the drum part of the rotor and in turn pulled the backing plate slightly outward. I removed the new rotor, lightly tapped the backing plate back a little and bingo no more rubbing.

Mike never have i heard that the drill rotor will make a noise..i wonder who else is going to pitch in about it

Ivan

if there is a point of contact - it should be reasonably obvious, no?

I believe there is a point of contact/ high spot on one rotor but it did not seem excessive. I will have a better look once things are apart and I can view both sides of the rotor and run a dial indicator over it on the bench.
I will get a look at the e brake assy and backing plate as well.

Same rattle
 

I have exactly the same rattle and have been throwing parts at it like crazy. It seems to be in passenger rear. Please, what did you find to be the source???