aerox rattling but dont what it is HELP PLEASE

hi i am new to scootershack but my aerox is rattling from the engine i fort it could be bearings ..but how wud i know without splitting the engine the head and barrel are fine ..but there is this muddy residue on the cylinder dont know what it is ....it is a pm 70 with a doppler crank ...there is no movement in the crank up or down or lest to right ...piston was replaced not so long ago and rings are fine along with the piston


help stuck