What is this strange sound in fuel rails.

I was adjusting my fuel pressure when I noticed what sounded like a vacuum leak in the area of the where the upper/lower intake meet and around the #1 cylinder.

Yes, the vacuum line that goes to the regulator was plugged!

I finished adjusting the fuel pressure and put the vacuum line back on and the sound went away.

So I pulled the line back off and plugged it and the sound came back. I started trying to locate it using a mechanics stethoscope but couldn't find it at any of the normal places you would look.

I placed the stethoscope against the metal fuel rails and heard the sound coming from there.

The sound is a hissing sound like a vacuum leak, but once I put the vacuum line back on the regulator, it goes away. Any idea whats causing it?

I thought bad regulator, but there is no vacuum sound coming from it, just the fuel rail, it holds steady normal fuel pressure and I observed no fuel coming out of it at idle.

Anyone know? Is it even something I should be concerned about?

Thanks

anybody??

Doesnt seem to have affected anything so Im sure its fine, just the 1st time I heard it and figured I better check. Thanks.