Curious if the Duramax used in the CV series truck has been having any Thumping sound issues at idle speed? GMC and Chevrolet 2500, 3500 trucks with the Duramax have this issue. I believe it may the cooling fan clutch causing this issue and would like to know if the Navistar part is different or the same GM part? The engine uses two accessory drive belts, one to drive the cooling fan only and the other to drive the alternator, ac compressor. Thank you for any comments or insight.