well new problem help please

well my truck is a dump truck cummins m11 with 14709ll trans..now the i call problem is when im loaded and going from 6/7 gear i have a litlle pop sounds like the pop that a truck makes when its running out of fuel...but it only does it once going from 6/7 gear when loaded...called talked toshop and was told to check it over for a hole in the tubing that goes to the turbo and the air cooler thats what it sounds like to him....what do you guys think it just started doing it yest. and only loaded....the pop sounds like its in the ex under the cab when it does it..i checked my mpg and im still pretty good on that almost 7mpg...i changed the fuel filter last week and used the same baldwin as always...going to change the air filter today....thanks