My 15 ecoboost is making a pronounced vacuum sound when idling cold and during acceleration. No check engine lights, nothing seems loose that I can tell. the vacuum noise I refer to is like a humming, the same humming you would hear from a vacuum cleaner,it mostly sounds like that at cold idle. I don't think i notice any power loss. what could it be? any experience with this noise. The car has a cold air intake FYI.