HARRISON TWP. (WWJ/AP) – Residents of a Macomb County community want to know how a black, oily substance ended up splashed on their homes, vehicles and property.

The mystery gunk was found Sunday in parts of Harrison Township, apparently after falling from above, according to the Macomb Daily.

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Residents have been told, WXYZ-TV reports, that the tar-like substance doesn’t appear to be harmful.

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Paul Schlutow says he first thought it was from birds, but it appeared too oily. It covered his pickup and dotted his driveway. He suspects it’s from aircraft.

The affected area is near Selfridge Air National Guard Base and located in a base approach path. Technical Sgt. Dan Heaton says the base is examining aircraft traffic records. Local authorities are investigating and plan to report findings to base officials.

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