I noticed yesterday after coming back from a 60 mile trip the fuel pump was humming and I mean really humming, not the light sort of humming one normally associates with an externally mounted fuel pump. And it was the same today. Now, I replaced the pump with a quality Walbro only 3000 miles ago along with the fuel filter, the only other difference is that I have in the last week filled the tank to the brim twice and let it run on both occasions to either a 1/4 or nearly empty. One other point that came to my attention is that the humming is barely noticeable from a cold start, it seems the humming is induced when the pump has run for a couple of hours. Normally, I would reckon the pump is on it's way out in the above situation, if it was an old pump but since it's not I'm at a slight loss. Anybody got any ideas other than a fault with the new pump? What has crossed my mind is that I've recently ran a lot of fuel through the system including two full to the brim tanks, is it possible that the fault is due to fuel filter becoming partially blocked, after using all that fuel suddenly it cleaned out the tank thus the pump is under pressure, gets hot and excessively hums?