After driving for a while in very wet weather, I parked. Later when I went to drive again I heard a loud, high pitched shriek from the passenger rear wheel area. When I stopped it would go away; in reverse, it became a scraping noise (like the muffler was dragging). It was so bad that my 9 year old daughter started crying hysterically because she felt unsafe. I stopped and inspected the rear disc, .... a number of times and couldn't find anything, and just before I was going to call for a tow I discovered a small rock stuck in the dust shield of the rear disc. When I removed it, the noise was gone!

Kind of a freak occurance, I think, but if anyone ever hears a similar noise, this may be the cause.

 

I had something like that that happen with my WRX. Thought I was gonna be driving on an axle stub pretty quick, then it went away.

 

I thought I was driving on a spindle stub once. Not fun. I was driving around the night before in a '69 Mustang in deep snow with a bearing cap missing. The next morning, it turned out the snow washed out all of the grease. 3/4 of the way to work that morning, the car suddenly lurched over to the passenger front, and smoke started rising from there at the next light. I limped the rest of the way to work, and when I got out, the tire/wheel was leaning at a 45 degree angle. On the night the first bombs were hitting home in Operation Desert Storm, my uncle and I were listening to the war unfold on the radio in the warehouse I worked at while we replaced the bearings.

 

How many miles on the brake pads? Could be the warning shriek that worn down brake pads give off when they are nearing end of life. There are little metal tabs on a couple of the inner pads that make the noise--and it is a LOUD noise.

 

There's a new brake set out for the RX-8 as well. I know because I took my car in for squeeky brakes, and they told me there is a replacement for it now.

 

When I test drove the 8, the drive went just beautifully. Then I pulled into the dealership lot, put it into reverse, and everyone on the lot heard that shriek. The sales guy came running out to see what I'd done.

A mechanic strolled out a bit later and found the small rock in the brake, just like you did.

Fortunately, that incident didn't stop me from buying an 8 later on.