* Wheel Bearing: This is a very common cause of knocking noises that change with vehicle speed/load. A failing wheel bearing often makes a pronounced knocking sound, especially when the car is idling or moving slowly. The sound could be less noticeable or disappear at higher speeds because the bearing is better lubricated under load.
* Suspension Components: Worn ball joints, control arm bushings, or tie rod ends can cause knocking sounds. These components experience more stress at idle and less under load (when the suspension is compressed by the engine). A front right issue would correctly locate the noise.
* Engine Mount: A worn or broken engine mount could allow the engine to move excessively, causing it to knock against something at idle. The additional stress when accelerating might lessen the knock.
* Alternator/Power Steering Pump: While less likely to be a knocking sound, a failing component in these could produce sounds that change with engine speed. Check for unusual belt squealing also, as this sometimes accompanies a failing component.
Troubleshooting Steps:
1. Visual Inspection: Carefully inspect the front right suspension components, looking for any obvious signs of wear, damage, or loose parts. Check the engine mounts for any cracking or excessive movement.
2. Jack up the Car: Safely jack up the front right side of the car and support it securely on jack stands. Rotate the wheel while carefully listening for any knocking sounds from the wheel bearing. Try to move the suspension components (ball joints, control arm) to see if you can detect any play or looseness.
3. Professional Inspection: Given the persistence of the issue after a recent repair, a mechanic specializing in older BMWs should diagnose the problem accurately. They have the experience to pinpoint the source of the noise and perform the necessary repairs.
Do not continue driving the car if the knocking is severe, as it could indicate a component about to fail completely. Ignoring the issue could lead to more extensive and costly repairs.
