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Have you looked under the car to see if any of the underbody air flow panels are hanging down, especially right under the engine area? You don't have a check engine light or any engine running issues do you?
If it is not running badly, then I am pretty sure you aren't having an issue with an engine hose coming off. I think the underbelly pan may have popped loose, as it needs to be loosened and refastened every time the oil is changed. Have you had the oil changed recently? If so I would bring it back in and have them check to see if anything is loose.