why does my BMW 3 Series E90/E91 make a whining noise when accelerating?

Solution

1. Preparation

• Gather tools and parts necessary for inspection and repair.
• Tools Required: Socket set, torque wrench, fluid pump, stethoscope.
• Safety Warnings: Ensure the vehicle is on a flat surface and securely lifted if necessary.

2. Inspect and Replace Serpentine Belt

• Sub-steps:
  1. Open the hood and locate the serpentine belt.
  2. Use a socket wrench to release tension from the belt tensioner.
  3. Remove the old belt and inspect the pulleys for wear.
  4. Install a new serpentine belt, ensuring it is properly routed according to the diagram on the engine bay.
  5. Reapply tension with the tensioner.

3. Check Power Steering System

• Sub-steps:
  1. Locate the power steering reservoir and check fluid level.
  2. If low, top off with the recommended power steering fluid.
  3. Inspect hoses for leaks or cracks.
  4. If leaks are present, replace damaged hoses or the power steering pump.

4. Check Transmission Fluid

• Sub-steps:
  1. Locate the transmission dipstick or fill plug.
  2. Remove the dipstick and check fluid level and condition (should be reddish and not burnt).
  3. If low, add the correct type of transmission fluid.
  4. If fluid is burnt or dark, consider a transmission fluid change.

5. Inspect Differential and Axles

• Sub-steps:
  1. Safely lift the rear of the vehicle and secure it on jack stands.
  2. Inspect the differential for leaks, and check fluid level.
  3. Rotate the wheels to listen for any grinding or abnormal noises.
  4. If any issues are found, replace the differential fluid or repair/replace components as necessary.