Usually people mention warped discs. More propable reason is that the discs have accumulated some brake pad material from sintered pads causing uneven friction. You can sand the discs lightly and try again. Unless you seriously want some posh wave discs. :fingure:
The vibration could be several things.
1) - pad material on disks(s). Surfacing the rotor in a lathe or grinder should fix.
2) - non-floating disk - not centering in caliper(s). Disassembling, cleaning, and lubing parts should fix.
3) - Disk warped - unlikely, but possible. Surfacing may fix, but rotor may need to be replaced is it is really bad.