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Matt, Mechanical Engineer
Category: Mercedes
Satisfied Customers: 22749
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have just bought a 2008 Aclass 180 and at speed i can

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Hi I have just bought a 2008 Aclass 180 and at speed i can hear a sort of humming but more of a whining noise from the rear left Wheel. If i lightly touch the foot brake while moving the noise stops. any ideas what it is please?

this sounds like a worn wheel bearing to me, when you press the brakes you take up the slack and so the noise stops
to double check this - jack the car up so the wheel is off the ground and shake the tyre from top to bottom and from side to side (with someone holding the steering wheel on the front) there should be no play in either direction. Any play in 1 direction will usually require a joint to be replaced, if there’s play in both directions then the wheel bearing may be at fault. If theres play only up and down its the strut top mount - to find this one you have to shake the suspension strut it self up and down with the wheel off the ground - so you may need to remove the wheel to check this one.
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