are there signs of coolant in the oil or vise verse? what color is the smoke? how bad is the smoke? another thing could be exhaust seals in the turbo are going out. check for oil leaks and boost leaks. it could be just something stupid. it doesnt necessarily mean its anything that significant. just check all the easy possibilities like boost leaks, oil leaks, turbo shaft play, compression, etc. dont go ripping the head off if there is absolutely no reason to pull it off.