Front disc brake noise only at high speed At a high speed (about 50km/h, but not sure exactly, as I don't have a speedometer) the disc starting to noise like it is touching the caliper/pad. At low speeds It doesn't noise and it's rotating free - it doesn't touch anything. It's hydraulic discs.
Is it a known issue for disc brakes? Or should one to replace the rotor / caliper?
What should I check for (all components are tighten well)?  

Edit:
It's front disc 180mm rotor. The noise is when going straight.

2 Edit:
@ Vorac &amp; starnger thanks for comments and answers, but it's looks like it's not the situation:
The noise is starting at some speed, and do not get louder it's the same all the time. The caliper and rotor are well adjusted (few shops checked it). The noise is even if I do not touch the brakes at all.
And it's not about lightly touching the pads - the bike is in use every day, and thou it's not downhill, it supposed to be already gone.
By the way, it's relatively new Merida bike, so the brakes should be in good condition yet.
If the disc is not touching (as you insist) then it must be the bearings. 
Take the disc out or pads out and verify.  

A more likely scenario is the the disc is indeed touching. 
At speed you get a higher frequency of touching and the materials heat up and expand slightly. 
With the expansion they touch even more and now the touching is audible.