This is a close-up of a Honda CBX1000 exhaust muffler. That line in the center of the muffler is not a weld seam. It is a buldge working its way out from the inside. Honda uses mechanical baffling in their exhausts. This means there are walled-off compartments inside the muffler. During combustion water vapor is created and this settles inside the exhaust, mostly at these barriers. Unfortunately, the water contains acids from combustion. Normally, the exhaust gets hot enough to burn this water vapor out and there is no ill effect. However, if the engine is not run enough for the muffler to dry itself out, then rust starts, hastened by the acid. This motorcycle has been subjected to that kind of treatment: short rides -- or worse, startups inside the garage, the very worst thing you can do to your exhaust -- and the deterioration is underway.