After you're sure the wheel is firmly the the dropouts and the QR is cinched down, put the bike into a stand and loosen the brake caliper bolts, spin the wheel and see if there's a way you can position the caliper by hand so that you don't hear any rubbing. If you find a position where you hear no rubbing--hold that position and have a friend or family member pull on the brake level while you tighten the bolts back up and see if that eliminates the dragging. (There is a inexpensive tool that's easily obtainable, the Hayes feeler gauge, that I like to insert between the brake pads and rotor before the lever gets pulled and the bolts tightened--although sometimes this isn't essential). Sometimes it takes two or three times to make this work.


If you can't find a position where there's no rubbing with a loose caliper, you probably will need to remove the brake pads and inspect whether the pistons are properly retracting. I've used q-tips with rubbing alcohol to clean the pistons and pressed them back in using the Park piston press tool--which is also inexpensive.


Usually doing these two steps is enough for me to eliminate the rubbing--at least for awhile. I like disk brakes on my cross bike--but they aren't totally hassle free.


I'm not sure about the quality control as a relatively inexpensive mech brake set and wheel, but the rotor/wheel trueness should be looked at if you can't solve the problem. Of course there are tons of videos that explain these processes--it's how I learned enough to keep the brakes from driving me nuts.