My rear disc brake makes noise when I ride fast I have a full suspension mountain bike with disk brakes.  When I ride fast, my rear disk brake starts to make a noise similar to the one you would hear when sharpening a knife.  It happens when I don't brake.  If I brake, the noise disappears, I only hear the smooth braking sound.

I presume something is wrong with the rear tire - visual inspection when it rotates fast shows that it wobbles.  I tried to demount it and mount it back again two times, but no success - still wobbles.

Can the non-aligned rear tire cause by disk brake to be noisy when I ride fast?

Shall I simply buy a new tire, or could the solution be elsewhere?

This is an update - with videos showing the wobbling tire.

https://youtu.be/_9Wor0KFL34

https://youtu.be/Bju-LyKCOi8

although it seems to be redundant now, as Jackson and Rider_X already suggested other solutions.  Thanks guys :-)
With disk brakes the disk rotor is attached to the hub and not to the rim so a wobble in the tyre is unlikely to be the cause of the noise.

What I'd be looking at is the following:


Are the rotor bolts tight?
Is the rotor warped?
Are the brake pads worn?
Is one or both of the pistons sticking?
Is the calipar aligned properly?


1 and 2 you can check easily.

For 3 remove the pads and make sure that there is at least a couple of mill of braking compound left and that the springs (if present) are in good shape.

For 4, with the pads removed check that both pistons are extended by an equal amount; alternatively with the pads still removed push the pistons back (carefully with a soft implement not a screwdriver) and then squeeze the brake lever, do both pistons move in and out evenly?  Be very careful not to push the pistons out to far! How you sort out a sticky piston is going to depend on the type of brake you have.

For 5 look at the disk rotor as you press the lever, does the rotor displace to one side?  If it does this indicates that the pistons aren't applying equal force to the rotor - this could be a mis-aligned caliper or it could be a sticking piston so you'll need to check 4.