On an orignal 600 pantah I once blasted up to Cat and Fiddle and on leaving a geezer handed me what looked like a 20mm spacer asking if this was from my bike. Nahh, not off mine mate and proceeded with speed the 20 odd miles home.
Next day found the right side engine mount was missing a bolt and spacer - oops.
Moral - check your engine mounts regular.
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