'98 Chevy Astro Fuel Pump

We have a 1998 Chevy Astro with 140K miles 4.3L engine. We replaced a fuel pump 9 months ago after the diagnose test showed that it's life was over. We replaced it with a Bosch Fuel pump which was kind of louder than the previous one in it. Also, for some reason it kept running for several seconds after the car engine was shot off. Anyway, after 9 months the car just suddenly died while waiting at the light. It was the fuel pump again. We went back to the store and since it was under warranty we got a new Bosch fuel pump (#2). This time it was even louder than the previous one, also runnig for several seconds after the engine was shot off. Each day it was running louder and louder, We went back to the parts store and ask the manager to come listen to it. He said he has never heard a fuel pump that loud and gave us another one under warranty (#3). Now it's installed, it's not as loud as the last one, but it's still runs a few seconds after the engine is shot off. We didn't really have a choice of brands, since they only carry this one. We agreed that if this one is going to get louder as well, we'll get our money back and will have to purchase a different brand fuel pump elsewhere. The manager at the store swore that they never came across this problem before. Do you have any knowledge about this problem with Bosch fuel pumps for Chevy? Any suggestions, anyone else wrote to you about this problem by any chance or are we the only un-lucky ones? Your comments will be greatly appreciated, thank you. George & Iveta