A170 Engine groaning noise

andyp33

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Jul 13, 2011
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A170
Hi
I have just bought a 6 year old Mercedes A170 automatic from my local dealer. Fortunately they gave me a 12 month full Merc warranty on it.
The engine when warm makes a groaning/low humming noise which almost matches the engine revs. In other words a slight delay. It sounds like a big belt fighting for grip on a pulley or a kind of air pressure build up being slowly released. sounds almost like a trumpet noise but lower pitched. It is more noticeable when driving slowly accelerating away from traffic lights etc. This is intermittent and only happens when warm. Merc dealer has no idea what it could be & I have insisted that they take it for a thorough test drive this time (not just two miles like the last time). I have ruled out the Air-Con. They have suggested that it is some sort of belt tensioner mechanism that needs changing & they are doing that next Tuesday. But even the technician said it is probably not that causing the noise.
I have only had the car three weeks & it is driving me insane.
I am going to take my camera out and make a video recording.
I am in need of advise please on what it could be
Thanks in advance.
 

dulayj

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Sounds like a belt related problem-hopefully they will look at all the pulleys for the poly v belt-check out aclassinfo.co.uk.
 

grober

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IS YOU CAR A W169 =LATEST MODEL? Mercedes-Benz A-Class - Wikipedia, the free encyclopedia If it is it will have a CVT [metal belt+ drive variable pulley system] automatic box----- this might explain the source of your noise? I would advise trying to get a drive of another A170 auto like yours That way you can see if the noise is normal or there is a potential fault/wear in the transmission. Possible ways to do this---- get a test drive at another dealer ------hire one for a day.
 

npuk

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6yrs old is a 2005 so W169.
 
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andyp33

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Thanks people, I will relay this to Mercedes Benz @ Loughborough who I got the car from & they are also taking it in this Tuesday to change a bracket type tensioner mechanism thing for the poly V belt will see what they say.
Once again thanks for all the input.
 
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andyp33

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Jul 13, 2011
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For info Mercedes have discovered the noise & it is some of the Hydraulic/oil pipes system when warm & under pressure creates as they said a Howling noise. Apparently they have a data/technical sheet on this issue. They will have to order parts in from Germany up to two weeks wait!
At least we got to the bottom of the noise.
 

dulayj

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Thanks for letting us know outcome-good to know your close to final resolution.
 

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