another air noise

[Four0Sport]

once in a while I'll hear little noises and think nothing of it. but this one is reoccuring enough to annoy me. sometimes when I start my 5.0 after it has sat for a while and put it in gear, either reverse or drive, i hear a loud woosh of air like a vaccum leak. my rpms raise slightly, around 500 rpm, after i start to drive the vehicle i stop hearing the noise or feeling an elevated idle. i cant find a common denominator for occurrence, i.e. weather, time of day, temperature. its just buggin me. i watched the IAC video and the noise isnt nearly that loud and by the time i put the truck in park and pop the hood its gone. checked the obvious things but to no luck. anyone else have/heard of this problem? thanks in advance.

 

[RubySlow]

once in a while I'll hear little noises and think nothing of it. but this one is reoccuring enough to annoy me. sometimes when I start my 5.0 after it has sat for a while and put it in gear, either reverse or drive, i hear a loud woosh of air like a vaccum leak. my rpms raise slightly, around 500 rpm, after i start to drive the vehicle i stop hearing the noise or feeling an elevated idle. i cant find a common denominator for occurrence, i.e. weather, time of day, temperature. its just buggin me. i watched the IAC video and the noise isnt nearly that loud and by the time i put the truck in park and pop the hood its gone. checked the obvious things but to no luck. anyone else have/heard of this problem? thanks in advance.

Could be IAC never know.. could be exhaust... check for leaks.. could be vacuum. Pump the brakes while it idles see what happens..