Exhaust sound from oil fill cap (crankcase).

Here is an answer that was posted a few years back to your question: Most engines now days employ an oil return/check valve in the pan that pressurizes the block, including the rocker/cam(app) cover area, and is normal. If you remove the filler cap, engine running, it will do exactly what you describe. If there was that much blow-by, there would be a CEL(app), fouled plugs, and pcv or O2 (app) issues all over the place. Even if there was blow-by, and the pcv valve was bad, removing the oil filler cap, engine off, would instantly relieve the pressure and you would see a lot of oil vapor. That's all. -----

should not be excessive blow-by at the oil filler tube, should be very little ( enging running and oil filler cap off ) if there is excessive blow by then it has to be the piston rings, were more then likely installed improperly, note: the gaps in the rings has to be staggered on the piston , course one would first check the PCV ( positive crankcase ventilation ) valve ..if it rattles when you shake back and forth then it;s okay..otherwise replace it.