Hello all,

I have a noise I'm trying to diagnose on a 2008 A4 Avant and I'm wondering if anyone would be able to lead me in the right direction as to what it might be?

These are my findings so far:

• It sounds a kind of like an electric pump that you may have for an air bed or in a pressure washer.
• Initially I was thinking of comparing it to a relay, but it's more of a vibrating sound that of the above.
• I'm in the UK, so my glove box is on the passenger side, but it's apparent from inside the car as much as outside, back deep in the glove box towards the engine.
• Whilst starting the engine it happens momentarily in short bursts before it seems to settle down and stop for a while, but then happens again occasionally whilst moving but also once stationary and even shortly after switching everything off. These short bursts happen intermittently for half a second or so, several times.
• A longer continuous burst can be triggered almost every time I spray the front windscreen washers, it seems for the duration of the spray.
• Enabling air recirculation or turning on the A/C can also triggers short, intermittent bursts.
• It is coming from around the fan that is below the pollen/cabin filter in the top right corner of the engine bay. I've removed the filter to see the fan and that seems to be spinning smoothly, but the sound is almost like it's just behind it slightly, not something I can access easily.

My question is, what potential culprits for such a noise could there be around that fan that may be electrical (A/C, washer related) or something that would trigger a vibration or pump (if that is what it is...)

Any help, thoughts and ideas would be much appreciated!

Thanks,
Ben