This is strange

[fishnmaine]

I searched in this forum for similar issues but couldn't find it but here it goes.
This sound is coming from the heater core area. Now I have no problems with heat or cold everything works fine. But this annoying sound. Now when you select a heating position you some times hear a flapping noise and grunting sound which is a door flap opening and closing. This is a light sound. The weird part is this when heat selector is off fan is off. Every 30 to 60 seconds later I hear this sound. Now when the heat and (fan set on 1) is on this sound never comes back on. I tried to explain this best I can....OH forgot this....When I shut the vehicle off key out this sound happens for about 10 sec. Weird or what..Any ideas out there let me know.


Thanks

 

[Blue91Ex]

if its a hissing sound when you shut teh truck off, its just a pump of some sort, someone told me it was the fuel pump or something..

 

[corkey]

it could be the vacuum coming out of the system,

if the heat is working fine, it's no big deal,,

 

[Ratbiker]

my trac makes the same sounds. i've been questioning these sounds for a while now. when the fan is on, and i shut the rig off, after about 10 seconds or so, theres a brblrlbrlbb sound. my guess is its a dry bearing or bushing in the heater fan.