engine knock

I just replaced a blown 2.7L engine last year in my 2001 dodge intrepid with a 3.2L out of a 2000 Concorde. Now over the past week, the 3.2L engine has developed a knocking sound at idle. The noise is noticable in park and neutral, and gets louder in drive at idle, and almost disappears in reverse at idle. The engine has 55,000 miles on it. I can't imagine it being something internal going bad already, because 3.2L's are supposedly very reliable according to just about everyone who has done this swap. It sounds like it could be a piston or rod knock. My mechanic friend told me to change the oil with 20w50 and a quart of Lucas Oil, and that should quiet it down and i could go trade it in on something else, because I don't want to mess with fixing it again if it's something bad internal. Could it be something stupid like the flywheel bolts? I read somewhere you're supposed to replace them when you take them out and do not reuse them, well I reused them with thread lock compound hoping that'd be fine, if they have losened, would that cause a noise similar to a piston or rod knock? I've driven the car about 10,000 miles since last year. The engine has plenty of power, no noticable loss of power, it idles perfectly smooth, and doesn't run hot. I was thinking it was a rod bearing, but the different oil made absolutely no difference in the sound. Any ideas?

Could be the Flywheel Attatching bolts or even the Torque Converter attatching bolts are loose or even possibly a cracked Flywheel. If you can get a hold of a Mechanics Stethescope, with the engine running probe around the bottom of the Engine Block and work from the front to the back and ending at the Transmission Bellhousing area, the area with the loudest knocking noise is where to start looking for problems.

And if you find and correct the problem get that 20W/50 oil back out of there, that stuff is too thick for that engine.

it was loose flywheel bolts. all better now, man am i relieved!