Geo-
What you are describing is what I labeled as turbo farting.
I took the coach to an International dealer, who kept it for a week.
They thought it was several things, and there were several calls back and forth to the factory to talk to the engineers. Finally, after intervention from GS and the referral to International, the Turbo was removed, and found to have excessive wear, after 1500 miles, and was replaced, under warranty. (about $2500 repair)
They also replaced the EGR computer, which deals with the exhaust portion of the turbo function, ergo, the farting that you hear. That was also done under warranty. (Another $900 repair.)
End result, the engine runs better, and now, I would say I have turbo pooting, rather than farting. Only occasionally do I now get the fart.
I have put about 8500 miles on the engine since the replacements.
Essentially, my repair dude, who was the staff expert on the engine, provided two observations that were of interest:
Everyone at International is awed by the engine set up- in that the engine is putting out 300 hp out of the 365 set up. No one in the shop had seen this configuration, and were surprised that the engine was getting 300 hp out of it. Ergo the turbo being maxed out, or close to that. I was essentially told that the farting was something I would just have to live with. I more in view that I am watching my turbo closely, to make sure it doesn't hemmorage along side the road one day. I earlier owned a Winnie View with a Mercedes diesel that had to power too much and was always going into limp mode due to a bad EGR valve, (well three times anyway, ) and was not a happy camper.
Further, they winked at me and sort of indicated to be very aware of changing the fuel filter every oil change, versus every other oil change. Something about fuel being slammed through at very high pressures to get that much horsepower through the block. I accepted that at face value, as opposed to them trying to sell more filters.
That's my story.... shortly, my pal and fellow Super Nova person Texas TC will view your posting, and share his wisdom I bet. He has a better grasp on the tekkie side of the story, and can explain better than I.
He will also probably mention that running the engine in the economy mode seems to help with the farting. I vouch for that.
I am a Super Nova Cheerleader, charter member.
JimBob
08 Super Nova
Greenwood, SC.
Presently off the road, will DW recovers from major back surgery.
Back out in December.
http://jimbobmissbetteandbuster.blogspot.com