Help

I have a ticking noise thats there with a cold start
and goes away once it has warmed up. It doesnt
miss and idles fine at all times. It has been using
maybe a quart in between oil changes. 2009 chevy
tahoe 6.0. Took it to the dealer. They told me it
wasnt a ticking noise that it was a knock coming
from the bottom and they needed to tear it down to
find it. They found nothing. No metal in oil or in
filter. Everything was in spec. Now they say its the
oil pump, so I asked it they ran a test on it and they
said no. Friday they ran the test and it was hight 58
at first then went down to 30-40. But are going to
let it set over the weekend and test it again. They
have now quoted me lifters as well but told my
warranty company they found no failers. Im really
confused on what to do. Sounds like they are just
guessing at everything and not really trouble
shooting. What to do?