First, easy test is remove belt and spin all accessories by hand. Also check bolts holding pulley on crank.
If you cant find anything there, start it for a few seconds and see if chime is still present.
If its gone, its one of the rotating accessories.
Still there, then start feeling around for loose brackets, linkages and clamps, like a muffler clamp for instance.
My l1501 developed a buzz- was a loose lens on rear reflector, thought it was a hydraulic problem......