Is it just in the spot where you are tying in to the other bead, or is it pretty much on the whole bottom of the pipe?  If it's just in the spot where you are tying into your first root stringer, you need to try a different runway grinding technique for the tye in.  It's all in the grind baby.  You need to make it like a ramp.  If your ramp is to steep, your root will be flat, if you make it nice and gradual, it will burn in there like you didn't even have a stop.  When running downhill, thats pretty much the only place you should have to feather on the whole root if your inspectors are gona nail ya for being flush.