Engine noise that makes my 2002 Saturn Vue V6 AWD sound like a diesel. Could it be a rocker arm that needs adjustment? If so, what repair cost am I looking at?

almost same cost.

Lifters, push rods and rockers arms. That's what does it. To check lifters. Start the engine and get it up to operating temperature. Put a half quart of transmission fluid in it and let it run. If the tapping goes away, let it run for about 30 minutes. Drain the oil and change the oil filter. Refill it and add some oil treatment first, lucus, slick 50.. what ever you prefer. If the noise doesn't go away. Look at the rocker arms and push rods, they should be polished, replace them as needed, I would still put the additive in.

most probably it is a wheel bearing,

I have a 2002 saturn vue. Same thing..sounded like a jet engine ...loud humming as I accelerated . It got increasingly worse. It turned out to be the front wheel bearings. Replace them, now the noise is half as loud...have to do the rears also! 93,000 miles on it. Also, don't forget to replace the timing belt. It it goes too long and breaks, it will trash the engine...

only the outside pulley needs to coime off not the cam belt sprocket ,from the sound of it ?? i feel you should entrust this job to the local garage because if you make a mistake you will crunch the valves into the pistons

Under the intake manifold,  it will need to be removed.  Not too hard to do for the average diy but recommend buying a repair manual as a guide.  you will need a 1/4" drive T30 torx socket with a long extension one of the bolts is hidden but the others are under the black cover on the top of the intake.  you will also need to remove the coil pack held on with torx bolts.  8 or 10 inverted torx socket needed for that.

Have you checked your wheel bearings? When these go out you can get a harsh grinding noise. This sounds like that is what it might be. Does it happen when you are going fast/slow turning/going straight? I know you said it's inconsistent but the more info the better. However, if I had to bet, based on what you have already said, it's your wheel bearings. Let me know if you have further questions. Thanks for using FixYa!

How do i check the transmission fluid in 04 awd v6 auto

Buy it new from many places Search Saturn Parts call local Dealer .
Happy Easter

No is not hard all you need to do is remove the tire and it haves four bolt on the back. one is kind of hard to take out do to not much space to work with.