Loose Nuts
Not joking, could be.
Check all fastenings on bars and bar end weights.
Then yoke, fork brace and wishbone business.
Then wheel spindle etc - haven't you changed wheels lately? Best check calipers and discs for warpage as well.
Are tyres knobbly, or worn road bias? Are you used to 200 miles on knobblies (think you are)
Just check for tightness, don't start tightening willy nilly.
See how you get on.