This usually happens when there is an "air" pocket trapped in the heater core. Make sure that the system is completely full and the radiator cap is sealing properly.
"IF" there is something wrong with the headgasket, combustion gasses will be allowed to enter the cooling system and will create the trapped pocket of "air". Other cooling system leaks will cause the system level to diminish and lead to this as well.
So first you need to do a cooling system inspection.
Jake... dude... you scare me sometimes. And thanks for the advice Vicoor, now I know what to check. Ive been hearing a different sound for a while now and just assumed it was because I turned my stereo down.
try burping the coolant system. park the truck on a hill, pop off the radiator cap (do this when the truck is cold, otherwise you'll likely burn yourself), rev the motor to about 2k rpm, and hold it like that for a little bit. (maybe a minute or two) this should help purge all the air from your cooling system.
release the throttle slowly, as doing so quickly can cause antifreeze to shoot out of your radiator. (and that's never a good thing!). top it off with coolant, put the cap back on, and see if it happens again.
if so- you have air getting into your system somehow. check all the coolant lines for pinholes (yes, a pinhole will do it), check your radiator cap like someone said, make sure your resivour is full, and if all else fails, do a leakdown test!
The check engine light went off after driving it a while. The truck had the headgasket,waterpump, and the timing chain changed right before I bought it. I changed the radiator cap the other day, so thats new. Would airpockets cause the temp gauge to fluctuate? I have a new Toyota thermostat to put in and then I will burp the system.Thanks for the info. If anyone else has any info its always apreciated.
I have the same thing, tried doing the parking uphill and running the engine until it got hot then putting the cap back on. didnt do anything, dont think I have a leak, not loosing fluid. I can hear it at idle, then when I step on the gas it gets worse. should I care? is the heater core going to take a shit on me?