I changed the oil in my gf`s car with Valvoline white bottle 10W40 (5 quart jug from Walmart) and noticed that the half quart left in the jug had this small gravel/particle looking stuff floating around at the very bottom. W-t-f is that stuff????? I just emailed Valvoline about it. I`ve never seen this with any oil I`ve bought at auto parts stores. Made me think about the old posts about people asking if Walmart sells substandard oils. What do y`all think? Anything I should be worried about or am I over reacting?