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Q: BMW 330d Rattling-Hissing Sound from exhaust side

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I have a 2004 bmw 330d automatic (steptronic) with an M57N (M57TU30D) engine and is making a rattling, squeaky-hissing sound from the exhaust side of the engine on idle. Started off a a minor faint sound but is now louder and sounds like a worn out clutch/ DMF. Sound is not coming out of the engine itself but outside towards the tranny. When the problem was getting worse, I was getting a yellow oil light after switching off engine and responded by topping up with a pint of oil but the light still comes on. Checking the dipstick would give me a normal level so I am no longer topping oil with the fear of adding too much oil. I also have acceleration and power issues when going uphill and have to resort to changing to manual shifting so that I can get enough power. I am inclined to think it could be vacuum-related but want second opinion and confirmation. Thanks in advance
My car has an automatic transmission.

A: Hey there. Thanks for writing in today abou...

Hey there. Thanks for writing in today about the rattling / hissing sound coming from your 2004 BMW. I experienced a similar issue and it was in fact a vacuum leak. However, there are several other symptoms of a vacuum leak that you should consider before diving in and buying replacement parts.

Typically, the hissing sound will be accompanied by a lack of power on acceleration, loss of fuel economy and in some cases, an engine misfire. If your car is experiencing any of the following, then I'd say the issue is definitely vacuum-related.

A worn out clutch will also produce several driving / performance loss issues, as well as commonly produce a rotten egg smell. If you need additional help looking at the problem, contact one of our local ASE certified mechanics, to pinpoint the cause of the hissing noise and make the appropriate repair.

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