Interesting weekend fuel pump problem advice please

I changed the fuel pressure pump regulator and o rings refitted new gasket new bolts job went well (I didn't need that skin on my knuckles anyway)
Then I changed my fuel filter not a really cheap one but about 18 quid but she squealed so I removed and sure enough had left the last top rubber gasket on so got rid of that refitted filter with just the one gasket and she still squeals
So I cut a hatch in the floor of the rear over the lift pump where the squeal comes from and in best time team fashion dug through the mud on top of tank and found lift pump ordered a new one on eBay but I'm convinced it's something I've done and that when it arrives on Thursday 9 th will still squeal it does run through its self bleed but then just sounds noisy engine runs fine been on some half hour school runs all good ,regulator doesn't leak now.
Any ideas? ( been in the workshop for 2 days now so my wife is starting to squeal like the pump but not in a good way!)

once you open up fuel system pump will squeal till system has rebled itself, removing bottom plug or switch on filter and placing a container underneath then switching on ignition will give an idea if pump screens are blocked or pump is failing

Thanks James I did that and convinced myself the pump was failing. The new one arrived today courtesy of eBay sold by JLS ordered on sun night cost 55 quid not bad .
So I removed my new hatch and tenderly tapped the holding ring in a lefty loosely fashion nothing oh bugger i thought so I had a cup of tea then got 15 inches of 1 X 3/8 and a 2 1/2 pound hammer and gave it a proper tap and round it went, pump then sprung up at me ,all good.
New one had gasket rubber thing on it as did the old one that came out ,so I just pushed it in and took up the slack and tried to tighten holding ring ,after half an hour I gave up and had more tea.
Then I took the gasket off the pump, it fitted nicely onto tank and fed the pump through the hole and tightened up easy. Connected pipes and power lead . Turned the key and ran round the back to listen, nothing just a faint hum. Oh bugger I thought ,fired her up started on the key ran like a dream.
I've had the truck 6 yrs now and that pump has been noisey as hell for 70000 miles still ran right up until today I assume it would have gone pop eventually but it's amazing what you think is normal
Anyway all done, thinking of selling the beast now isn't that always the way...

Those pumps have all got little personalities of their own and make different noises. I had a quiet one that I replaced with a noisy one and then that went wrong and I'm back to a quiet one, that's quiet in a different way to the first one. And so on.