Internal rattle sound

Re my rattle, using a stethoscope, the rattle turns out to be from inside the muffler, seems that there is a bit of material loose inside it.

Once in a while a baffle inside the muffler can break lose. Time for a new muffler.

garfield langille wrote:

Re my rattle, using a stethoscope, the rattle turns out to be from inside the muffler, seems that there is a bit of material loose inside it.

Good catch! That could cause a sudden random blockage of exhaust flow resulting in loss of power and engine damage. It pays to be attentive to little things and take time to investigate them.