The bracket is held on w/2 bolts just below the headlight. I suspect 1 is loose where it bolts into the bottom triple tree. I have this problem w/my bike time to time even w/locktite. I just check mine yesterday and the one bolt was broke off. This will be a pain to get out and replace.
Assuming that since the turnsignal AND driving light is vibrating, and if you have the Suzuki OEM lightbar, check the little set allen screws holding the round rod, that is under the center plastic chrome piece. (That, is a run-on sentence) the mounting might me tight but the round rod might be ready to break off and dangle your lights.
A few weeks ago while on the interstate I thought I saw my right front turn signal vibrating too. I have the OEM lightbar. Then this weekend I looked for it and noticed it was indeed vibrating but only at higher speeds and also seemed to be effected by the road surface (damned rain grooved concrete). It now also looked like the spot was vibrating too. I was able to move the right spot mount a bit too. Yesterday I took the cover off to check the allen screws and sure enough one of them on each side was loose. Ironically the inside set screw on each side. I tightened them down, can't move the mount now and I'll wait and force myself to ride on the interstated to check it out.
a little more info. no oem light bar. home made bracket. it is tight and the allen screw cant get any tighter. I heard the metalic screech when I stopped. I may just have to try to brace it better I guess.