T350 musical fuel tank

[non_linear]

I had the car out yesterday and when I parked and turned the ignition off it sounded like there was still a pump running on the rear n/s. A lot of pressure was relieved when I (carefully) opened the fuel filler, and the noise disappeared. Close the filler and very quickly the whine comes back.
I see this has been discussed on here before and it seems to be considered normal. I'm curious whether this is due to a partially blocked breather, or indicative of something going wrong!

[Alan_D350]

I had this on Sunday too. Never heard it before, so went to check 30 mins later to see if it had stopped (it had), so I put it down to the hot conditions. Also interested to know the cause..
Had about 15-20l of fuel left in there for what it's worth.

[non_linear]

I had a similar amount of fuel in the tank too, and a hot day. As I understand it, unused fuel from the fuel rail is returned to the tank, so a small amount in the tank will have a low thermal mass and heat up faster. Graham Varley mentions adding insulating washers to the fuel rail to reduce it's temperature, maybe for this reason.

[shep1001]

Tank vent blocked? next time it happens remove the fuel cap and release the pressure & see if it stops.

[ChristianMH]

Mine does the same esp after long hot drives where I use a fair bit of fuel. When I open the filler cap I get a big release of pressure and clanking noise - presumably from the tank walls popping in or out. It looks like air/pressure releasing out rather than in. How is the pressure in the tank controlled?