Blocco A Spiral
01-08-2007, 08:54 PM
Hello all, I've recently bought a used A6 avant 1.9tdi (AJM engine) which is going just fine apart from a strange intermittent noise and I'm wondering if anyone can help identify its origin.
The noise only seems to occur at idle and is a regular low frequency thump accompanied by a short rasping sound, it does this about 3 times a second and is not directly related to engine speed. It goes away as the revs increase but does not necessarily increase in frequency. The rasping noise seems to originate from behind the oil filler near the top of the engine.
I got the impression that it was caused by a release of pressure somewhere and figured that the only place that has any kind of air pressure at idle is the brake servo circuit. When I pump the brake pedal the noise goes away.
I haven't had time to investigate yet but was hoping the someone may have an idea what might be causing this. The car doesn't drive any differently.
Also, and this might be normal, when the engine is switched off there is a hissing noise from the brake servo/ back of engine area that continues for a short while. Any suggestions ?
The noise only seems to occur at idle and is a regular low frequency thump accompanied by a short rasping sound, it does this about 3 times a second and is not directly related to engine speed. It goes away as the revs increase but does not necessarily increase in frequency. The rasping noise seems to originate from behind the oil filler near the top of the engine.
I got the impression that it was caused by a release of pressure somewhere and figured that the only place that has any kind of air pressure at idle is the brake servo circuit. When I pump the brake pedal the noise goes away.
I haven't had time to investigate yet but was hoping the someone may have an idea what might be causing this. The car doesn't drive any differently.
Also, and this might be normal, when the engine is switched off there is a hissing noise from the brake servo/ back of engine area that continues for a short while. Any suggestions ?