Fuel Pump Noise (not a hum)

Actually, I'd say more of a fuel tank.

I just recently installed a walbro 255 lph pump, following all instructions. I put everything back together just as it was when I took it apart.

Now I find when I undo my gas cap when the tank is nearly empty, I get that pressurizing hiss, since I have had that in another car, I considered that normal. What is abnormal is sometimes during driving, I will hear the tank do that same hiss with the gas cap on.

I am a bit concerned if my tank is creating a vacuum, which would cause the pump to work harder, shortening its life.

I also have a FPR to install that I haven't yet, but I was under the impression that since ours is a return fuel system, having a 255lph with no regulator wouldn't hurt anything.

Some tips/advice would be very welcome.

No codes yet.

No carbon canister. The line that used to go to it now sucks open air. It could be that valve connected to it now that I think of it.

Exactly how does the carbon canister work in terms of the fuel tank. It was my understanding that it was there to help alleviate some of the pressure within the tank by letting it vent a small bit of gas out.

Maybe my tank is pressurizing and not creating a vacuum. I'll have to check the next time I take the fuel cap off and see if it is a blow or a suck.