My bet - its a loose recoil assembly as that produces the most 'noise'.

remove the recoil unit (if you KNOW how) and attempt to wiggle the 'stub' of the shafting coming out of the top of the engine. If wiggle, suspect top crankshaft bearing, etc.
If no 'wiggle', then examine the underside of the recoil unit for 'crash marks' as sometimes the recoil unit bolting can come loose and the recoil assembly can then crash into the cowling, due to the now 'bad alignment' due to the loosened bolting etc. All this is painted 'dark'/black so the crash marks are easy to visualize.
Use high temp. Lock-tite on all the threads of the recoil assembly.