Im not sure which one you have but the one i have is a 1 piece cover. When i first looked in my rearview mirror and saw it "wiggling" in the wind i was concerned. I examined how it is constructed and realized its just going vibrate. I just check the screw that holds it on every so often to make sure its still on tight. I have had mine for about 6 or 7 months and no problems, but it defintely vibrates in the wind. Heres the one i have:
Also, i dont have foam piece, nor did i ever(unless in threw it away not knowing what it was)