possible valve chatter?

[OleYellarGT]

Ok, so this morning the temp is around 30*, I started my stang and heard what sounds like valve chatter or some sort of slight knocking sound for a period of a minute....is this a product of temp and oil? I know I need to change the oil today, could that be it? Guess I will change the oil and see if this continues.....any other ideas are gladly welcome....thanks in advance