BMW E90 Makes Funny Sound On Alternator When Starting

Started by Virgo · 0 Replies


4 yrs

Posted: 3 w
There are a couple of possibilities for the funny alternator sound on your BMW E90 during startup:

Worn or Loose Serpentine Belt: This is the most common culprit. The serpentine belt connects the crankshaft to the alternator and other components. If it's worn or loose, it can slip and squeal when the engine starts putting a load on it.

Alternator Bearing Failure: The alternator itself has bearings that can wear out over time. A failing bearing might create a whining, grinding, or scraping noise during startup.

Overrunning Clutch Issue: The alternator has an overrunning clutch that allows it to free spin under certain conditions. If this clutch malfunctions, it could create a clicking or whining noise during startup.

Here's how you can narrow down the cause:

Listen closely: Does the noise change with engine RPM? A belt issue might change with RPM, while a bearing or clutch problem might be more constant.

Visual Inspection: Open the hood and look at the serpentine belt for signs of wear or cracks. Check for any visible damage to the alternator itself.


If you suspect a belt issue, it's a relatively inexpensive fix to replace the belt. However, this should be done by someone comfortable working on cars. Alternator bearing or clutch failure is a more complex repair. Consulting a mechanic is recommended for diagnosis and repair.
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