Engine knock
 

I have a 2001 5.9 Cummins with about 40,000 miles on a rebuilt engine. Over the weekend I was pulling a heavy RV and got a strange knocking noise. It increases with engine RPM and is more noticeable at lower RPMs. It is more noticeable near the driver side front wheel well and in the driver seat. I don't have any codes and haven't noticed any issues with performance. Any help will be greatly appreciated.

How is your oil pressure? Pull your dipstick and check oil for metallic particles. If you have or can get a mechanics stethoscope, listen to the lower end and then the top end. A failing or failed fuel injector will knock loudly and sound seemingly like a rod knock.

First of all, thanks for the input.
Oil pressure is good and no metal on the dipstick, no performance issues have came up and the engine is running normal except for this knock. I was trying to find a friend of mine's stethoscope in his toolbox this morning and after digging around his hodgepodge I started to hyperventilate and had to try the next best thing, a screwdriver.
I crawled under the truck this morning and the sound seems to be more noticeable underneath, I've read a few post about the flexplate but didn't see any Remedies for it. Any ideas on that?

Well whereas a screwdriver does kinda work, ya cant beat the ol stethoscope for true pin-point diagnosing. with a stethoscope you can put the probe directly on the part you want to listen to, like each fuel injector line or other entity you suspect. Sound travels through metal really well, and that can be quite decieiving. Sorry bro, but I have no input on the flex plate.

The only way I know of to fix a flex plate would be to drop the trans and go from there. But that's a ton of work just for something that might just he in your head.