new fuel pump noisy

[Ken Jones <kenjones@alaska.net>]

Replaced 4kq fuel pump at 135k miles as a precautionary measure because 
it was noisy. For a few months it "sang" then the sound became a mild 
buzz then it became a noticable buzz. Installed a new Bosch pump, $165 
from GPR. Noise went away. Now a week and 500 miles later, the new pump 
is louder than the old, just noticable when cold, and "angry wasp" when 
hot. Can anyone offer a plausable explanation other than the obvious 
(defective new pump)? Filters were replaced at 120k miles at scheduled 
maintenance.