Chevrolet: Engine Making Noise, chevy lumina, wt oil

Question
The upper part of the motor is making noise.  It's a  '91 Chevy Lumina Euro.  3.1 Lit.  V6 Engine.  It sounds like the noise is coming from the tappet or lifter.  I took it into the shop and they think it might be something with the oil; they said the oil is not getting up into the higher part of the engine.  They only way they can find out is if they tear it all apart, and that costs a lot in labor, just to find out that they can't fix it or that it was a simple problem.  What do you recommend I should do?  Do you have an idea of what the problem is?

Answer
hi;
 ok this is the easy thing to do change the oil and filter
and use a good heavy duty oil and add a can of stp oil treatment. Does the engine have a lot of miles on it , the lifters / or valves could be sticky  or have a lot of old dirty sludge on them and not getting oiled enough there are a lot of things it should not cost that much just to take off the cover to look at the tappets etc. and even adj. them if possible. but the oil change should do a lot
I would use a good 30 wt. oil w/ a can of stp.