Well, she's back. Rear end links are nice and tight again, surprising how loose it got without realizing. Feels and sounds great again over rough sections of road.
In terms of the 'awesome' diesel sound? No leaks found, and it went away. Now all that remains is the tick from the injectors.
Soooooo... I'll keep an eye on it. From what they said, the day after I dropped it off, the rattle/diesel sounds stopped and then sounded like a "puff puff puff puff" at the speed of the engine idle. Then that too went away later that day. I picked it up yesterday, drove home on the highway (albeit not mashing the throttle, but regular acceleration) no sounds but the tick tick tick of the injectors.
Ah well, no mechanical issues is all I care about
tanks empty, time for some Shell v-power and test out the race tune after I've given it a few days to ensure all is well.
Thanks again for all your help guys.