Moaning Disc Brakes? My Disc brakes have been shuddering all day (been riding most the day). And when I say moan, I mean like I can feel the bike shudder up to my rear end. I tried the trick where you rub mud on them and brake hard a few times, and that made them stop shuddering, temporarily. I think the reason they are shuddering is because I recently took out the pads and cleaned them. I also cleaned off the rotors with some simple green. I'm not sure I bedded the pads in right, because I've never really done so before. To bed them in I just braked hard a handful of times after re-inserting all 4 of my cleaned pads. The pads are in good condition, as they have those little gold sparkles. I checked the calipers, and everything looks good. I don't think they're contaminated, as the rotor is clean. 

Update: So here's what I've done: scrubbed the pads off with an unused toothbrush, cleaned off the rotors with isopropyl alcohol, and bedded in the pads properly this time (dousing the rotors with cold clean water each time!). Yet it still moaned. The reason I say that past tense is that in adjusting the worlds most nonadjustable mountain bike somehow the brake cable has gone completely slack. I can't even tighten or loosen it on my bike (diamondback overdrive sport). I tried adjusting the calipers, nope. To adjust them, one has to loosen them to the point where they just wobble around or have them so tight that the pads rub the rotor. So yeah, I'm probably going to have to take an expensive trip to the bike shop.
Sounds like dirty pads to me, but disks can be a pain to de-squeak.

The things I'd check are...


Clean the rotors with alcohol, brake cleaner or a bottle of ethanol from the chemist.
Remove and reinsert wheels. Make sure the QRs are nice and tight, and the wheels are straight/centred properly.
Check all the bolts holding your callipers to the frame/fork are tight enough.
Rotor bolts too.
Try and bed the pads in again, 10-20 hard stops should do it.


That should do it really, if it doesn't try new pads on clean rotors. Bed them well.

You could also try lightly greasing the back of the pad where it touches the piston and sanding the pads down, cleaning the rotors, and bedding in again.