Vibration after Truck sits for a couple days

[Hrspwr88]

Hey,

As the title says, if my truck sits for 2 or 3 days I get a vibration that feels like the tires have flat spots or are out of balance. Within a couple km the vibration will ease up and eventually go away. I thought it was the OE Goodyears as I know several people complain about them. But after changing to my winters it still does the same thing. Its pretty bad at the beginning, feels like the tires are square...
Does anyone else notice this Or have any ideas on what it could be?

 

[cj7]

You got it right: Tire flat spotting. Tires with nylon in the construction do this more than others. Also happens to heavier vehicles sooner. Colder it is, the longer it takes to go away.