It also heavily depends on the year of 4BT or 6B that you use. the mid 90s to late 90s one were notoriously loud. the ones from 89-93 werent near as loud. and then the 03s and newer when the switch to the common rail injection system quieted them down a ton. You can swap from the electronic CP3 pump to the 12v mechanical P7100 pump or even the A pump for the 4Bt. Course that'll add substantial cost but would give you the mechanical injection system without the noise of the early and mid 90s cummins.
I've also found that sound deadening really does help a ton as well. Also, most people when they are swapping in these things, are welding up solid mounts, often because the factory cummins mounts are HUGE. about a 6 inch diameter rubber mount, and then probably another 6-8 inches for the bracket.. Dodge and Nissan as well as the box trucks and such are designed for that extra width and height. But non designed cummins vehicles don't have that room in MOST cases. It is also one of the reasons why Ford declined the 6B, too wide and too long and they didnt want to change the frames or engine bays to accommodate it. But without that mount, its gonna shake the crap out of you
