wfieldin If you have no clamps to hold your fuel line it is rubbing inside the tube. I have seen this happen from the vibration of driving. If you are going to leave your fuel line inside the main tube, get a can of Great stuff and fill the tube to stop the line from moving inside. Check the line before you do this. A frame full of gas could be a real interesting ride one day.
Rick L. Ps we do this with 4 wheel drive hill crawlers for both battery cables and fuel lines.