ram 1500 5.2 auto no mods 115000miles

ok this is my problem, i hear a puff puff sound whenever im driving my truck on the road andthe soundgets faster as i accelerate. when the truck is in park idling i dont hear it even if i rev the engine there is no puff puff sound. for what i know it is not a tic tic sound[8D]it is more of a puff puff sound, for what i can tell the sund might be coming from under the drivers side but icant check this since when i hear this im driving on the road and is kinda hard to look under my truck when im driving down the road i dont know if this makes any sense, but any help would be apreciated.