The combos must be quieter, I've never noticed mine. I can hear it if I really listen for it but not at any other time. I've never seen anything about this complaint either.... just be glad it works.

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k