I changed the filter about a month ago. It didn't have any effect on the noise. I thought that might be the case, but it wasn't. It actually sounds louder after the filter. More of a high pitched buzzing, than a bogged down rumble.
The reason the pumps are so loud is that they run at 60psi or higher. If you were to pinch the return line the pressure would hit 150 in a second. I dont understand GM or the other car man. as they put huge pumps then regulate them down to 60psi. By the way thats why they die 5 times as much as 5 years ago. My 16psi pump is still going strong at 200,000. By the way some new cars trucks are not even using regulators they are using a variable ground in the ECM to contoll pressure. Im sure glad I got out of the buissiness in 96 as all the crap on the new cars is cool but the labor prices are and will have to reflect that soon.