Originally Posted by Black Dog

It does sound like head bearings to me. Get the bike with the front wheel off the ground and turn the bars from side to side. Anything other than a smooth, silent glide is corroded or maladjusted bearings. It isn't a huge job, perhaps 2 hours for a competent mechanic, but I would get it done as soon as possible. I had the same with my Triumph Sprint and I continued riding it thinking I would sort the issue out 'later'. Then, on a low speed manoeuvre on dust and gravel, I dropped it.