Need help with a 2015 Freightliner dd15 harmonic vibration

It doesn't do it under full power?

If you are say half throttle, and it's doing it, then mash it to the floor will it go away? If so, slowly or rapidly?

 

Had a similar noise but it would get loud enough to drown out my radio.
I have n14. I replaced the harmonic balancer and the pulley on crank shaft.
I didn't have much vibration but it was loud noise that would come and go randomly.
Good luck.

 

Ask Freightliner if your front cab mounts are the "latest and greatest"....had a brand new unit with a vibration and Freightliner sent out a Field Engineer and found they had updated the cab mounts - problem solved after checking and re-checking everything like you.

 

Now is this vibration road speed or engine RPM sensitive? Like when it occurs, can you drop/grab a gear to change RPM while holding the same speed? What happens?

 

Mine is like that also but Im not hearing the sounds you are.

 

Just listened to the audio file, that slapping sound you said is coming from the bunk, can you feel it?

Sounds and vibrations can be real a nightmare to figure out. The problem can be on one end of the truck but sound like it's on the other end.