The Nissan Path

I have rattling noise coming from the engine that gets louder after the engine is warm. I have not been able to pinpoint the exact location but it seems to be coming from the front passenger side, maybe middle top. I am mechanically inclined so I can do the work myself I just can't seem to diagnose the issue. It's a 3.3 with 149k. It is a sot rattle almost marbles in a can sound. Thanks for any help!

Did the noise start all of a sudden or come on gradually?
Did you have any overheating incidents or any issues with the lube oil system? Have you tried going to a heavier weight oil to see if the noise changes? Have you done a diagnostics check?

The noise has come on gradually, I have not changed oil weight but did change to synthetic blend sine I bought the truck 2 oil changes ago. I have not ran diagnosis since I do not have a light on. I have put a little Lucas in it but have not noticed a change.

When the noise gets louder as the temperature comes up it can be a few things oil related because the oil loses viscosity, or bearings expand and increase clearances where the oil cushion becomes less effective.
If you're correct about where the noise is coming from then you could get lucky and it might be a collapsed hydraulic camshaft follower or it could be piston related like a wristpin. If you're wrong about the noise then it could be connecting rod bearings. A compression check might help narrow it down.

The noise does not get louder with higher engine speed so was thinking it might not be lower end related. Please correct me if am wrong!

Higher engine speeds tend to result in higher oil pressure so, noise would not necessarily increase.

With the engine running, try disabling one cylinder at a time to see if the noise goes away or lessens so it can be isolated to a particular cylinder (this can be done by removing one spark plug wire at a time or disconnected a fuel injector harness connector).