You sure it's not just the turbo still spinning a little bit after shut down? It can make some funny noises at times with the blades still turning a bit.
2005 F-350 DRW 6.0PSD Longbox
CrewCab 4.10's and a Limited Slip - Nicknamed "TINY"
B&W 5'er/Turnover Ball on top, better MPG than my half-ton 155,000+ on the clock
SCT X3, DJ's Diesel Performace Looney 160,Tow 50 and Econ 40 Tunes
Autometer triple pillar with Trans, Boost and Pyro Ultralite II's
4" Farmboys exhaust with cat delete
ARP studs installed and EGR Valve welded by Scott @ Trucks Unlimited