Engine noise

[rs74]

I have an 03 2500HD with the 6.0l. I bought it with 80,000 on it and now has 148,000. It has always had this noise since I bought it. If I am driving in town and am on a street that has stop signs every block I hear it the most with the windows down. I take off from the stop sign and then at about half block I left off and then I hear the noise. It sounds like lifter noise or maybe piston slap? Not really sure which or what it is. It has never got any worse but I am curious as to what it might be.