I have a 2006 2500HD LBZ Duramax which I really appreciate, having moved from a 6 ltr gas. I use the truck mostly for pulling our camper. I am experiencing a noise under the truck. It seems to occur under the truck on drivers side under back seat. It occurs once, maybe twice a day when I'm pulling grade or when it is pulling harder than usual. The noise sounds like a puff, little explosion, air release brake, ---? The local garage doesn't know what it could be. Does anybody have an idea what this is and how to correct it. Thanks

Do you have a boost leak on the driver side intercooler pipe boot? I would start there