Simmer, I have heard the same sound on mine, more of a whistle when the engine is pulling at about 50. It comes and goes. I have been told it is a plug missing in the air box. I did find a rubber plug in my driveway after I washed it last year sometime, but hav'nt checked the box to see if it is missing or not. I'm not too wooried about it, but I believe it is definetly an air associated noise and not bearing or grease related. AI is removed and carrbs adjusted.
