-98 Astro Fuel Pump

I recently purchased a used 98 Astro Conversion van. After a couple of
weeks the fuel pump started making a high pitch noise while it was running (sounded like the bearing was going bad). I installed a new fuel pump assembly (AC Delco, cost $300). Now the noise is back intermittenly. Is there a "pressure relief valve" that bleads off the pressure when the engine is idling? The noise goes away when I accelerate the engine so I'm thinking it may be related to some type of pressure relief problem.

I'd replace the fuel filter if you haven't done it when replacing the pump. A dirty filter will make pump motor work harder at pushing the fuel, affecting the pump noise and life!