I think I know exactly of which you speak. Is it the fuel inlet hitting the pipe? On my '06 FE450, the exhaust has a shooting marble sized divot in the pipe so as to clear the fuel inlet of the carb. Your '05 has a different pipe I believe. Also note that a 550 or 650 will have the carb placed a bit further up, the engine is taller. I wouldn't feel too bad about placing a divot in your pipe to clear the carb if needed. It is helpful to get a clearance between the pipe and carb anyhow, to minimize heat transfer.