Rattling noise at around 2200 RPM? on 2004 BMW 325Ci

Happens when accelerating/decelerating - always right at 2000-2200 RPM. Most noticeable from a stoplight, accelerating in traffic, but have heard it at high speeds as well. They thought it was a problem with fuel pump & even replaced the entire fuel tank under warranty to address issue, but it is still there?

Asked by for the 2004 BMW 325Ci