98' Tahoe engine knock at lower RPM's, HELP GM Merlin!

My 98' Tahoe has a light engine knock or ping at about 1500-2000 RPM, normal cruising speed. Ran a snap-on scanner on it, got no codes and also checked while i was driving, operation of the knock sensor, it would show a maximum retard of 4 degrees when the truck is a full throttle and anywhere from 1-2 degrees at cruising speed. Ignition timing is at 28 degrees cruising with no load and dips to 17-18 under heavy load. Voltage for sensor is 4.75. So right now I'm not sure what to do, truck has 133,000 miles on it and everything else seems fine.

Any help is greatly appreciated!!!! :screwy: