Weird noise????

[Shed]

Weird noise from under the truck. Sounds like it is surging with the engine, happend immediately after start up. Shut down and crawled under, nothing leaking or out of place. Almost sound like a puff of air escaping, around firewall on the pass. side, not really up in the engine area. Truck sat for about 18hrs. and low was 7 degrees, not plugged in and sitting at an odd angle (listing to the pass. side). Once she warmed up the noise was gone. What's anyone/everyone think? Not worry just cold? Had no problems since and running awesome! Thanks for any imput. I'm probably just paranoid....
Shed

[More Power]

7 degrees is pretty cold. A diesel will start with more effort and will exhibit slightly different sounds and characteristics when started that cold - more so at even colder temps than 7. I'd not worry about it if the behavior doesn't show itself at warmer starts (say 30 degrees or higher). :)

Jim

[petestoy]

7 degrees is not that cold mine typicaly sits outside at -10 degrees F to -20Degrees F. It is not plugged in all the time, i don't always have access. The truck does make some wierd noises (poping, whisling, gurgling) typically right after startup, but they go away rather quickly.