Jimidiguana

Over the last month that I've had a new rigid fork on my mtb, a scraping noise has been getting progressively worse. I used to only hear it when I was standing out of the saddle and putting power down on climbs, but now it's constant and much, much louder than it was before. I can tell that the rotor is slightly out of true, but I'm also concerned that something else with the wheelor fork might be what's causing the noise. Does hub spacing affect the way the rotor can align in the caliper? Any help is appreciated!
Here are a couple short videos demonstrating the noises that the front brake is making. This Image is taken with the bike flipped over, so the scraped part is the part of the caliper is the part closest to the ground.

dsbrantjr

First rule of troubleshooting is to fix what you know is wrong before going further.

tyrion

If the wheel connects to the fork with a skewer (as opposed to thru-axle) sometimes when you reinstall the wheel it can be slightly off - skewers just aren't as precise as thru-axles. Sometimes I have to jiggle it and put some pressure on it (push the wheel into the fork) to get it aligned right.

That looks like the source of the noise. You might need a new rotor, judging by the amount of abrasion seen there.

delbiker1 

Disc brakes are a terrific improvement for bicycle brakes, but they can sure be a thorn in ones brain and ears. How old are the rotors and the pads. If you are sure the rotors are out of true, it would make sense to start there. Adjustment of the pads may be necessary, as well as adjustment of the cable. You can always pay the man at the LBS.

Andrew R Stewart 

The photo sure looks like the rotor is rubbing the caliper body. The vids have what I think are two different sound sources. #1 is the rhythmic noise a rotor with vents/holes can make as it rubs against either the pads or the caliper body. #2 is more like classic (a questionable term for so young a technology, as in disk brakes) brake squeal. On second look/listen to #2 I now think the squeal might be rotor/caliper body contact.

When the different fork was installed was the caliper also readjusted to be centered over the rotor? How warped is the rotor? (A near impossible answer giver that the OP likely doesn't have a dial indicator or set up to use it to measure, so more a judgement answer WRT other rotors that can be compared with). Is there another wheel with rotor that can be temporarily swapped to test with? And lastly (for now) has an experienced sset of eyes had a chance to look at the set up? (Usually meaning a LBS but not excluding non pros). Andy

jp911

Looking at the scoring on the mounting side of the caliper, you might have a stuck piston on that side which is warping the rotor when the opposite piston is doing most/all of the compression on the disc.

SClaraPokeman

Re sound #1 in my experience has been easy to rectify. I will remove the brake pads and resurface them with a mouse type sander and then clean the caliper using alcohol taking particular care arouooond the pistons and its seals (I like to use Q-tips for that). Then I reinsert the brake pads and loosen the caliper bolts, spin the wheel and try to by hand align the caliper to ascertain the metallic rubbing can in fact be eliminated. If I can make the sound disappear, I'm then confident I can make the needed adjustment. I'm very partial to my Hayes feeler gauge which I recommend for caliper adjustments. After the wheel stops moving, try to hold the caliper in position and insert the gauge's blades between the brake pads and rotor, depress the brake lever so the wheel is locked, then tighten the caliper bolts gradually between the upper and lower (I sometimes wish I had three hands for this process, but I've always been able to make do with two). I've always been able to clear this annoyance using this process--although I sometimes need a couple passes.

My only encounter with howling like in video #2 was when I inadvertently got silicone spray on the rotors. Cleaning the rotors with alcohol made the sound go away. I didn't have to replace the brake pads although they can be contaminated and cause howling.

Good luck. I really like the self adjusting properties of good disks. I rarely have any issues with them.