I realize this is an old thread, but it was helpful to me today after having this exact problem!

I noticed after some track time this morning a speed-dependent scraping that came from both back wheels. As mentioned above, it sounded quite a bit like worn pads grinding on the rotors, but I had fresh pads.

Sure enough, the rear brake protection plates that had warped a bit into the rotor. I didn't even have to take the wheels off to fix the problem... Just reached through the wheel spokes and pushed the shield away from the rotor a tiny bit. Noise gone! If the problem repeats after the next track day, i'll just bend them again or possibly just get rid of them.

[Warning! Should be fairly obvious, but make sure you let your brakes cool *way* down before you go sticking your hands on or near brake rotors!]

By the way, Porsche OEM protection plates [aka backing plates, dust/heat/splash shields, etc. ] are only about $10 each, so no worries about buying unbent/unwarped ones down the line if you decide you don't like your 'custom shaped' plates!

Part #3 in the diagram, 996.352.801.01 for non-S/Turbo rear brakes.

 

Wow, I have also been having this problem for the past several weeks - scraping/rubbing sound that occurs at speed one or both of the front wheels, I couldn't tell which. I had my tires rebalanced, no change in sound. I started to wonder if the sound started about the same time I replaced the pads and if I screwed anything up.

I have custom wheels and reached my hand in between the spokes with a stubby screwdriver and pryed the shield back from the rotor on the passenger side. Then I went to do this on the drivers side and out dropped a small pebble - LOL.