I've been hearing a humming sound from the rear of car even when everything is shut off. I found it to be pressure in my gas tank. When I removed the cap, it stopped.
Is this a problem? I have a new MB cap which I believe is not vented
(124 470 0005)
I can also hear my fuel gurgling in the tank when I start engine and gas starts to circulate. This a new sound.
Does it sound like fuel pressure regulator going bad or something?? Or normal?

It's an 87 300E

Thanks

Angel