98 LTZ Engine Knock

I have a 98 LTZ 3.8. Recently I had the lower intake gasket and the upper intake replaced. In the last few weeks I started noticing a knock, which *sounds to be top-end, but I do not know for sure. My oil has not been changed since my mechanic replaced the gaskets, though the level is OK. I think it could have something to do with the cheap oil that was put in, but I'm not sure.
Is this something I should address right away? It isnt a bad knock, but I dont want to make sure I dont get any permanent damage.

Can't source the knock from here, could be the coolant contaminated the old oil and damaged bearings, get a tech to listen to it for a diagnosis.

The oil was changed at the time of the gasket replacement

I'd recommend an oil & filter change using what you usually put into the car. Give it a listen and if you still think you have a problem, get a mechanic to hook up an oil pressure gage to it, then start it from cold. Also have him try to pin point the problem if possible using a mechanic's stethescope.

Bob

Thanks for the suggestions.

I did notice that I do not hear the knock when it is started cold. When I drive for about 5 minutes I can hear it.

Then I definitely agree with Maxwedge's diagnosis. But do get it looked at really soon in case it is the bearings. Some coolants really do a number on bearing-face material.

Bob

Well, changed oil and filter this weekend and it didnt seem to improve much. I am taking it in asap. Engine seems to run really smooth , but i still hear the knock/clackity clack, especially when accelerating.

Well, took it to a mechanic for a quick look...
Just listening to it he thinks there is a collapsed lifter. He said it's possible that it could fix itself, or i could try to clean it up with a little bit of trans fluid in the crankcase.
To fix it he said the intake would need to be taken off again and the whole deal would probably cost me around $1000. Does this all sound legit?

Trans fluid or Marvel Mystery Oil will sometimes get a cranky lifter pumped up again...it may have just ate some crud from the gasket job and may clear itself out.

I used to have an old Ford LTD that had one lifter that would tick like crazy once it idled down sometimes, and I found if I shut it off, waited about 15 seconds and started it up again, it was fine....otherwise it would tick the whole drive...strange. So predictable and easy to deal with, I never investigated the cause.

The thing I wonder about, is it seems from your description that the orifice in the lifter is stuck open a bit, so once the oil warms up and thins a bit, it doesn't hold enough pressure to stay pumped up...I'd try some detergent in the oil and give it some time. unless it's a really hard racket, it's probably not going to hurt anything short term..

Just thought I would fill you in on the final diagnosis... I replaced the lifters, which didnt help. I ended up selling the car to a buddy who works at a GM garage. He tore the motor apart and found a bad rod bearing. The notch that keeps it in place was completely worn off and the bearing was spinning around the crank I guess.