I have a 2002 tahoe that ive owed for 5 yrs +. I noticed here lately that when i 1st start her up for the day that it is knocking until it idles for a bit. then its fine for the day. does it sound like it could be a lifter losing prime? It has 40lbs + oil pressure when warmed up. she does have 260,000 on the od. just looking for any suggestions.