It's most likely to be the steering bearings.
Checking if they're loose: put the front brake on hard, and wobble the bike back and forth, while feeling with a free finger to check for any movement around the top bearings.
Checking if they're tight: You (still) have a centre stand? Put the bike on it, and weigh or tie down the back, or jack up under the exhaust so the front wheel is securely lofted. Turn the handlebars side to side, feeling very carefully for "notchiness".
If either of the above is true, time for new bearings. Not terribly expensive, in the UK go to
www.bandcexpress.co.ukIf not, it could be your fork bushings, they often get neglected. My bike needs them replaced, I know, as it has a knock around the front that is 100% not the steering bearings. I intend to leave it until the fork seals require changing though, then I'll do the whole job and get the lowers powder coated.
