Fuel pump questions

[Aleksander Mierzwa <alex@matrix.pl>]

Hi List,

I have a problem with my recently replaced fuel pump (new Bosch unit). At
the beginning, it was very quiet (one could barely hear it even from
outside of car). Now, approx. 2 months later, it is getting louder - much
louder. The sound is not the high-pitched "buzz-whine" the old worn pump
was making, but rather a lower "howling" noise. This howling is accompanied
with another, hard to describe, "screetching" sound. Both get somewhat
quieter as the car warms up, but nonetheless, it's easily audible over the
engine noise at idle. The noise is also "fluctuating", eg. it constantly
changes the pitch and volume, sounds like an electric motor with worn
bearings (???). So, my questions are:
1) Is it normal and I should live with that?
2) The pump was very quiet when it was about +10 degrees Celsius outside.
Now the temperature dropped to about -2. Is the pump supposed to be louder
when it's cold outside?
3) Could I make any mistakes during installation that caused the pump to
get louder soon after? The job went smoothly.
4) Is it posssible that the pump is currently just breaking in and it will
get quieter over time (I only made something like 500 miles since I
replaced the pump)?
As usual, any input appreciated. TIA

Aleksander Mierzwa
Warsaw, Poland
mailto:alex@matrix.pl
87 Audi 5000CS turbo (mine)
88 Renault Medallion wagon (mom's)
91 mountain bike (just in case both cars broke at the same time :-)