The past week or so in the DC area it has been, on average, around 27 degrees and snowy in the morning and lower sometimes at night. On several occasions i've let the car sit for atleast a day and a half because 1: LS's are not the best vehicle to drive in the snow and 2: wanted to give it a rest and drive my girlfriends car to do maintainence on it while she was away. After the sitting i noticed upon starting the car i could hear a slight tap for maybe 30secs then it disappears and becomes normal. Car has 93k+ miles on it and ive been using Mobil 1 5w30 for the pass two oil changes. Is a slight tap normal for this scenerio or is there something to fear?