"Could be a lifter, but should
"Could be a lifter, but should be making the noise all the time. Could be a injector problem. My mechanic says this is ruled out by loosening each injector while running and making the noise; retighten and go down the line. If it is the pump it might involve the cam. The RPM suggests the turbo because it kicks in at about this rpm. You could listen closer to the turbo with a scope or screwdriver end and feel any vibration to check bearing noise, or remove aircleaner and rotate turbo by hand (with engine off) and check for roughness and play."