for a while now when I start the truck up I get a sound that almost sounds like a cooler does when you are walking with it. the sound of the ice in the water swishing around. only a little lower in tone.

The sound seems to come from the two center vents and only last for a couple seconds then goes away, does not happen every time.

I don't notice anything else about the truck while it's happening (loss of power ect.)

any ideas?

I thought vacuum leak, if so where do I start looking? how do I even check for one? sounds like something simple a mech. will charge an arm and a leg for.

 

You either have a small leak somewhere and have air in the cooling system, or there is some debris in your vents or blower motor.

 

+1 for air in the cooling system. That'd be my first guess.

 

+1 for depris in the vents. i went camping and left my truck parked under a tree for a week and came back to a similar noise. i cranked up the a/c and out came enough leaves to make a small structure out of.

 

i've had leaves fly out at me too. i also had that foam from the vents come out in little chunks.

 

do you mean the engine cooling system or in the a/c?

my air works fine, I have had it cranked up all the way and nothing has blown out at me

 

air in the cooling system, you'll hear a gurgling/running water type noise behind the glove box when the air rushes through the heater core. when my heater core was bad it didn't leak out of the evap case and the only way i knew it was bad was when the windowshield started fogging up and had a film on it.

you can try to bleed the air out (if that is whats causing the noise) by parking with the front end up on a hill and running the truck with the radiator cap off for a little bit, while adding coolant every time the level drops below the top of the radiator.