Lo,

I have a strange issue with a UK MY00, 45K on the clock.

Whenever it idles in traffic n the fan comes on at least twice, thereafter there seems to be a very slight but noticeable knocking noise coming from I think the left hand side of the engine. Car was serviced and mot'd recently with a clean bill of health from a dealer. When this happens performance seems to be very slightly down, but not anything bad.

Weird thing is when it happens and I go and listen to the engine I cant hear this knocking noise at all. I can only hear it inside the car. But it definately seems to be engine noise and not for e.g the heatshield or something moving around.

The other strange thing is it only ever happens on a certain route into work. If I take another route and again let the fan come on twice whilst idling in traffic it doesn't happen at all

If I'm driving around normally and the engine fan isn't used, then this phantom noise doesn't happen either, and car performs as expected. Fuel consumption, oil, water levels are all ok.

Any ideas on what it could be, before I log it as possible problem with the dealer. Failing MAF? Worst case failing bottom end? Car is under warranty still, so would like to diagnose if it is a serious problem.

 

Do you happen to drive past GCHQ at Cheltenham on your normal route?

 

Erm nope, I work in Swindon, why?

 

Is it to do with your air con?

If it is specific to a particular route it does not sound very serious and might be a supernatural phenomenen.

 

I'd ask these guys

 

Nope aircon not being used atm.

scooby_matt, Your pic link is dead But I got the gist from the url