I have a M1078 with a CAT 3116 and at idle notice vibration coming from the motor sometimes. The cab seems to amplify the vibration and make it more noticeable as the door panels make noise against the door. If I give it some throttle the vibration goes away. I don't feel it while driving unless I'm stopped or moving slow (at idle rpm). With my foot on the brake when I shift to drive or reverse it makes a little more vibration than when in neutral. My throttle pedal does stick slightly so to get the rpms down to idle I push up on the pedal with the corner of my shoe. I can feel it through the cab when inside (fyi, my air ride does not work yet) and when out side if I put my hand on the bumper, etc. I don't know if this vibration is normal or not. This is the first diesel truck I've owned. I did a quick check to make sure the compressor bolts were tight, flywheel bolts tight and noticed very minor play in the fan. Let me know if you notice this in your trucks or if I should check something else on my truck.
I made a couple quick videos to show you what I notice:
https://www.youtube.com/watch?v=4Vyd_2vTCLc
https://www.youtube.com/watch?v=DVUhe9-YyJY
I had the door open in the video, so its not as noticeable, but good view of the inside of the cab (it was still light out):
https://www.youtube.com/watch?v=pTKsdrylpIQ
I made a couple quick videos to show you what I notice:
https://www.youtube.com/watch?v=4Vyd_2vTCLc
https://www.youtube.com/watch?v=DVUhe9-YyJY
I had the door open in the video, so its not as noticeable, but good view of the inside of the cab (it was still light out):
https://www.youtube.com/watch?v=pTKsdrylpIQ