Flap, Flap, Flap...what is this sound?

[FAST4DR]

Maybe it's me, but I have noticed a very distinctive FLAPPING sound lately. Gas mileage while towing to and from races, also, has gotten HORRIBLE at about 9-10 mpg towing only 8000lbs (roughly). Sound is much more noticeable at idle. FLAP is probably the best way to describe it, but it almost sounds like valve tap, too. Truck has 42k on it. Any thoughts?

 

[BigGunZ]

Have you noticed any change in boost, EGT, or smoke? A valve tapping sound can easily be an injector.

 

[FAST4DR]

EGTs do seem to climb higher than usual.

Seems to be smoking LESS than it normally did (with CL program on)

Boost holds steady at 28psi - I was seeing closer to 30

I checked codes and only P602 is showing up.

 

[BigGunZ]

If you happen to have a infrared thermometer gun you could read each individual exhaust temp at idle (since it happens at idle) and see if it's an individual cylinder problem.

 

[jelag]

My 04 3500 dually made a sound like this... . when you drove down a street with a wall of buildings so the sound would bounce back into the cab with the window down..... it turned out to be the U-Joint in the front axle. We pulled both and changed them... one was rust and the other was fine... we installed greasable u-joints... . please not ""not the front drive shaft"" but in the nuckle of the front axle...