When u press the brakes, the pads clench the discs the resistance and friction hamper the spinning of the wheel.
Over time, the brake pads wear out and do not necessarily maintain their shape. Most of us don't change brake pads regularly, its more of a "use till it dies" phenomenon.
These out of shape brake pads thus do not have proper contact with the disc, and they cause the disc to become uneven. This causes vibrations when u brake, because two uneven surfaces are making hard contact at a relatively high speed.
Due to this, it is a good idea to tool the discs when one gets new pads. Mind u, a lot of blokes will try using sandpaper on your discs to "tool" them, but I'd recommend the proper machine for this purpose. Most Suzuki dealerships have them.
When you next change pads, go for disc tooling and brake service also. The vibrations will vanish.
Its a minor issue tbh and nothing to worry about. Its just a nag.
Sent from my GT-I9500