Could also be a slightly bent rim. I had a bent rim and didn't know it until one day I heard a strange growl and vibration at certain speeds. upon acceleration, my traction control light lit up. Thought the egine had problems but it was just a bent rim.

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Current: '11 135 E88//6 Speed//Silver//Black//M Sport//Prem//Cold//Sat//Smrtphone Int

2008-2010: '08 335i E93//6 Speed//Monaco//Saddle Brown//Dark Burl//Sports//Cold//CA//Sat Radio//ED

2005-2008: '05 330 E46cic//6 Speed//Jet Black//Black//Sports//Nav//Cold