Disc brakes are squeaking I bought a new bike that has mechanical disc brakes. They were squeaking really hard. I tried aligning the caliper. Now the squeaking noise is gone form the front brake, but not from the back brake. I noticed that the brake in the back has less space between the disc and the brake pads, but that shouldn't be a problem. The brake pads are new and so are the discs, and I cleaned everything. What should I do?
Ugh! Bicycle disc brakes are not without their weaknesses.  The frequent attention and adjustment they require due to noise or pad rub is particularly irksome to me, closely followed by the system's ridiculous intolerance to pad contamination (really?  That sort of flaw considering the environment they're to be used in?), the recommended &quot;fix&quot; being pad replacement.
Park Tool's mechanical disc brake tutorial is one of the best discussions regarding mechanical disc brake set-up, alignment and trouble shooting I've seen.  The best advice I can give you is to watch the video and/or go thru the text.
A couple pointers: 1)often times when there is noise or rubbing that won't go away after resetting the caliper alignment, if you  re-do  the alignment loosening only one of the caliper fixing bolts, it helps to quiet the problem. 2) a disc brake rotor needs to be trued more often than people realize.   Brake noise that's refractory to resetting the caliper almost always has rotor issues at it's heart. 3) the value and importance of bedding in new pads and rotors is often understated. Learn how to do it correctly.  AND DO IT! 4)don't use the brake lever's barrel adjuster to tweak the pad distance in a mech. disc system.. These are only for countering cable stretch. 5) be mindful of the contamination issue and keep oils, greases and your fingers away from the pads and rotors. Keep rubbing alcohol on hand and use it to clean pads and rotors often. Use a clean rag for this.