Strange Impact? Noise

Hello, everyone. On my way home from the office recently I was entering
a limited access highway in my 2011 Ford Focus when I encountered what I
thought was a heavy object striking the side of my vehicle. I figured
at the very least I should have a large dent(s) on the side of my car
but a subsequent walk-around of the parked vehicle revealed nothing.
There wasn't any debris or other objects on the road at the time of the
encounter. Perhaps something happened under the hood but the vehicle
appears to be behaving as always. I know this isn't much detail but
this has me baffled. Thanks for your time and any comment. Sincerely,
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J. B. Wood e-mail: