I have a 1997 F-150 with the 4.6L. I have a weird noise that comes up at the most random times. I was able to get it on video when the truck turns off, I caught the last 4 seconds but it will last for about 10 seconds after turning the truck off. I have not been able to create the noise, I have tried hard braking, soft braking, turning the wheel quickly, slowly to max turn. I am assuming this sound is from something pressurized, so i am assuming brakes, steering, cooling. It could be a vacuum leak maybe. I hear it willing driving sometimes, its really the most random times that i hear it. I have disconnected the brake booster vacuum line and i am not able to recreate it. I will be smoke testing this spring when it gets warmer out. Any help would be helpful, this sound has me stumped and my brothers who is a certified mechanic.

 

I can't hear anything in the sound clip but If you are running air conditioning or your heater on defrost, the a/c system can make a hissing or depressurization sound as the high and low side temps evens out. Could also be a vacuum leak in the vacuum reservoir or HVAC system.

-Dan F

 

Thanks for the reply. I am familiar with the A/C or heat decompressing. This sound is not that. I will try to fix the video upload.