What causes whining when accelerating but stops when off gas

Hi, this is Bo, an auto expert on RepairPal's Car Genius team! A whining noise when accelerating that stops when you let off the gas in your 2001 Mercedes E320 could be due to a few things. It might be a worn serpentine belt, a failing alternator, or even a transmission issue. The noise getting louder with acceleration points to something engine- or drivetrain-related. As for the radio, the “CODE” message usually means it’s locked and needs an anti-theft code after the battery is disconnected or power is lost. You can find that code in the owner’s manual or get it from a Mercedes dealer. If you need any further advice or want help finding a trusted RepairPal shop in your area, please feel free to call us at 877-913-1554!