Generator belt rubbing on timing chest bolts
Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models
You may find that your generator belt rubs against the two top bolts on the timing chest cover.
Thanks to Ralf Brinkmann for posting this information on the old Yahoo! Loopframe_Guzzi news group (which has now moved to Groups.io). In Ralf's own words:
If I remember right I used 6 mm screws with Ribe Allen head (DIN 6912) - a special Ribe Allen key with guide pin is available for that head type.