I have a tapping or ticking noise coming from my engine? Ive had this truck for about two weeks and was told that this noise was not normal.the person I got it from told me that it was rebuilt about 16000 miles ago.it has 163k on od.i was also told by a mechanic I could take off the serpentine belt to see if it was internal prob.is this advisable? im thinking its either a timmimg chain or a hydrolic lifter problem? it dosent miss hits on all4. what could it be?