Well after 3 years of it sitting in my garage not moving, I finally got round to taking my XB12R to a nearby mechanic because it was making a horrible noise.

I checked the primary chain and oil pump gear and they were fine, although I did find this youtube clip ( https://www.youtube.com/watch?v=lE-1zbiWIaI ) of a similar Buell making the same noise. By the time I got it to the mechanic is was a lot louder, and wasn't sure if I was going to make it...

The mechanic has completely stripped the engine down expecting to see it in a bad state, but he cannot see anything obviously wrong. As much as this may be good news, he is reluctant to put the bike back together without knowing why it was making such a noise in the first place. His only guess would be the hydraulic lifters...

Unfortunately the chap in the youtube clip did not find out the cause either, so I'm really hoping that someone here could give me some pointers?