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Hello TT universe… I've come across an interesting noise, and I can't quite pinpoint exactly what is causing it. It's a metallic pinging noise, it sounds like it's coming from either the front or top of my cylinder. It happens quite loudly at low rpms, especially when cold, however it does seem to continue even once the bike is thoroughly warm and ridden for a while. I uploaded a clip of the best audio i could get to youtube at this link : You can really hear it around the 4 sec. mark. The bike is a 2004 husqvarna cr125, 75 hours on the current vertex piston, 19 on the ring set. I run 91 pump gas mixed at 28:1 with Torco GP-7. So as usual, I decided to hit my marks to see if I could figure out what was going on. Pulled the top end apart and inspected the piston and spark plug for signs of a lean condition. Piston head shows clear carbon build up right around intake ports, and less build up around exhaust ports, which kind of makes sense. Picture also attached. Spark plug is chocolatey brown. Does not appear to be excessively lean, so I feel like it may not be detonation? Performance wise, the bike is not at all sluggish or boggy. Very responsive and smooth under heavy acceleration and when I need to access mid-rpm torque up through over-rev. This bike also eats up exhaust o-rings with the FMF pipe. I've adjusted the metal tabs for the rubber damper mounts on the expansion chamber, and since then its not as bad. I checked over the exhaust system before the tear down and all bolts were tight, exhaust was securely in the cylinder. I was thinking maybe it could be the exhaust rattling around. Maybe the piston is worn past tolerances and resulting in extra noise? Anyone have and ideas?