Slight knocking ..should I be concerned?

My 92 Seville has a weird knocking problem......
when I start it up it uns quiet ...although ruff (needs timing or tuneup)
After about 3-5 minutes Iget a Knock-knock-knock sound that increases with RPM ..

Is there somethig I can do without a rebuild...cause its kinda anoying and im concerned if its doing damage or not?

Thanx

Is it a loud knock, or softly as it idles? The 4.9s were known for main bearing thump. There is nothing wrong with that, just a noise from the crank going up and down on the #1 bearing from being under load with the accesories.
Describe it more and I may help you out! Also what weight of oil are you using? Should be 10W-30.

It is louder in the car when I have the windows rolled up....
It is quiet enuogh that if i have the blower on or even the radio at 10+ I can hear it...
When I pop the hood it sounds like its comming from the front side of the engine...
It does sound like its on a single cylinder cause at idle its about 1-2 times a second ... when I speed up it gets faster and the road noise drowns it out at 30(KM/H)

Its just frustrating pulling up to pick someone up and it sounds so loud to me...
Oil is 10-30 ...and I even tried that "knock stopper" stuff but nothing.
I am assuming synthetic wouldnt help?

i suggest putting a very tiny amount of transmission fluid in with the oil this should solve the problem .. this is commen practice among used car dealers because most the cars they get have been sitting in car impounds or auction lots for a long long time an things dry up so they put the tranny fluid in to rebuild everything an some times this fixes the problem permanently an other times only temporarily