I have a 98 ram 1500 with the 5.9 and on the passenger side right below the door a little further towards the back of the truck is sounds like, the best way i would describe it is like "pat pat pat" its not loud by any means or anything, its just an annoying noise, if a passenger is going to get in to the truck i always get a "whats that?" it almost sounds like its coming from a small black box under the passenger side door, any clues on what this could be, or what the small black box is?

i guess theres a possibility there could be a small exhaust leak too, i just havent cared enough to crawl under and check :P

 

It sounds like maybe your looking at the evap canister. Just lay under it and grab the black box your seeing and see if its loose, if you ever 4x4ed the truck, that evap canister could have hit something due to the fact its pretty open to hit things. iv done it a whole bunch if times with my 98.

 

+1 on the Evap canister. It might be cracked or a hose is off or damaged. But if you can't be bothered to look under your truck for 2 minutes and maybe take a pic, are we suppose to guess what's wrong? Geez