Mysterious 'surging' sound

[KeithS]

Here's an odd one: once warmed up, my 2010 1.6TDI produces an odd 'surging' sound at idle – it's akin to the sound a fuel pump might make if it's cavitating and, from the driver's seat, it appears to come from the engine bay, or dash area. It's a low-frequency sound that you cannot hear anytime other than at idle and is not a constant sound, but a pulsing. The interesting bit: if you turn the air-conditioning on and then back off again, the sound disappears for a few seconds before gradually returning. Air-con on, sound disappears. Air-con off, sound gradually reappears. If it had been the other way round, I'd have said it was the air-con making the sound and probably in need of a charge or new compressor but as the sound only appears with the a/c off, I'm stumped.

BTW, you can't hear the sound from under the bonnet – mind you, all you can hear is the TDI engine doing its thing anyway. The guys at Celtic Tuning had never heard it before and wondered if it was anything to do with the EGR valve, but who knows. Car has done 32K miles.

Any ideas?

[fleagal]

A wild stab in the dark but could it be a cooling fan from the head unit? I had a similar problem on an Audi A3 - the head unit would warm up, the fan would come on and the sat-nav DVD (2009 reg) would fail to function after a fashion. This was possibly caused by cables fouling the fan thus preventing the necessary cooling.

It might be the case that the air-con would remove the excess heat and the fan stops turning? As I say, a wild stab in the dark..

[gaza1994]

hmm - i have a few posts on here regarding the same issue i think - one of my posts have a video of the noise, be interesting to see if it is the same thing and if you do come to a resolution regarding it.