Help me understand oddly specific brake noise

2006 Volvo V50. On a route I drive several times a week, on one - and only one - twisting downhill stretch that requires mild brake pressure to control speed, the right rear brake begins to make a pronounced oscillating noise, as if something rotating is rubbing intermittently on something that isn't. Performance is unaffected, and the noise resolves itself within a half a mile or so. There are other downhills with similar inclines and curves on the same road that require similar braking, but these never cause the noise to occur. Nor do I hear it on any other road in any other condition. Everything on that corner looks normal, but I have not disassembled it. Any ideas? I'm torn between voodoo curse by someone who holds a grudge and that the road construction disturbed an Indian graveyard on that spot.

Probably a bit of pad deposit on one spot on the rotor that has a slightly different coefficient of friction.

I bet if you take the rotor off you can see a "ghost" of a pad on the front or back.

Or, a hardspot in the rotor.

I got nothing.

Heat buildup.

Pads are getting grippy with heat but they are not being applied hard enough to keep from vibrating.

You could try pulling it apart and making sure anywhere the pad contacts the caliper or carrier is well lubricated (meaning, lube the carrier, lube the pads where they contact the caliper) which should make the noise go away.

I have also had weird heat related scraping noises caused by rust ridges inside and outside the pad contact area.  When the brake rotors get hot they also get larger in diameter, so the ridge on the bottom can rub against the pad.  Likewise, I have had cold rotors make noise from the outer ridge until things warmed up.

Sounds like I need to pull it apart, inspect, and lube, at the very least. I'll get in there when time permits; if nothing else, I'll have to pull the wheels to swap to snow tires in a couple months.

In reply to 02Pilot :

Another thing you can try, right now, is to scrub the rotors clean using the brake pads.

Very simplified, cold pads remove metal from the rotors, hot pads transfer material to the rotors.  What you may be hearing is areas of higher pad transfer on the rotor, as noted earlier.  We can try to address that without lifting a wrench.

What I like to do, which probably horrifies some people, is brake hard and firmly one or two times in the morning while everything is dead cold.  This scrubs the rotors.  Key is to get heavy braking in before you get heat into things, so you wipe the rotors clean while the pads are still abrasive.  If you engage ABS, it's too much   My brakes don't get rust buildup, they don't pulsate from uneven pad transfer, and they don't make weird noises either. 

I have "fixed" noisy brakes on customer cars this way, but without regular scrubbing the noise eventually comes back.

I just had a weird  brake noise resolve itself on the Molvo. Every so often there would be a slight "clunk" noise when I hit the brakes. Not always. I looked a few times but  with nothing obvious put it under the category of : "I will know what it is when it breaks properly"

Then one of the bolts that holds the caliper to the spindle abandoned ship entirely; just backed out and made it to ditch-bolt freedom. It tried to warn me but I never clued in. No harm but I went around the four corners and checked the rest of the caliper bolts.

In reply to Pete. (l33t FS) :

I'll give that a shot and see if it helps. I am not shy about using my brakes firmly, though rarely so when dead cold.