I have a new 2003 dually cummins.

Love the truck. Noticed a nasty drone at 2000 rpm -

becomes especially apparent in 6th gear (about 110km).

Two dealerships have no idea what is making the noise and

say that others have complained of the same.

Just "Harmonics" they say. To me it is very irritating and

happens at just the speed I want to go - so I am always

battling it.

Anyone out there heard it or know what it is?

Thanks big time in advance.

6TH GEAR HAS A DIFFERENT ANGLE CUT PATTERN. IT WILL MAKE NOISE TILL THE EDGES WEAR IN. KEEP THE OIL CLEAN.