I had a leak on my return line for the fuel where it connects at the fuel rail. I tried to drain the fuel pressure down using my fuel pressure gauge. It was at 10 and took a long time to go down to zero. I then removed the gauge from the schrader valve and it was making a hissing sound and appeared to have air and fuel coming out together. It did this for over 5 minutes and went away. I had the return line disconnected at the time so it wasn't coming from the fuel return line. Is this normal and the car had been sitting for 3 hours? It was in the 60's today so could this just be pressure from the fuel tank?