Is anyone elses Duramax LMM or other engines doing this???

At idle, the exhaust tone changes between two distinct levels and frequencies. It sounds almost like someone is covering the exhaust opening at the tip; then uncovering the exhaust opening at the tip. It cycles back and forth every 5 - 10 seconds or so.

Variable turbo.... and egr

Regen going on. The more you drive the more you know whats happening.

Regen going on. The more you drive the more you know whats happening.

His truck doesnt regen:rolleyes: read sig
I think egr

I think he is already DPF free so no more regens for him;) it is the turbo vanes opening and closing

x2

Ahh to be DPF free, check on the vanes.

my lbz does that i have noticed:)

Ditto on the VVT.

I here that too, since day one so I never worried about it.

;) it is the turbo vanes opening and closing

Yup, :exactly:

I believe we have the answer.

Thanks to all who responded.

tuned mine out with efi so no more hiss:D

The hissing is a whole other sound I hear coming from the exhaust tip at times. Is that also caused by the change in the turbo vanes, or is that something else??

same thing as before .depends if trucks cold tuners and what not. u can tune it to kinda sound what you want if you work at it . mine just has one nice deep steady rumble

FIRE0021- What vane angle are you running? are you experiencing an occasional rough idle?