[Obertelli]

Yesterday, and totally out of the blue, my right-hand drive 2002 2.7 Tiptronic S started to make an odd noise.

It's an electronic squeal/hum (difficult to describe) which lasts almost three seconds and repeats every five minutes without fail, and it comes solely from the right hand dashboard speaker.

The sound varies in volume going through cycles where it gets louder and then goes back to being very quiet before gradually getting louder again. It occurs with the PCM 1 stereo unit switched on or off and also occurs when my wife and I have our phones turned off completely (was hoping they were causing some kind of interference).

The sound occurred in daylight when the lights were off, at night with the lights on, and functions like the climate control and heated seats made no difference to it.

It's such an oddity that I'm at a loss to identify a cause, it's tempting to blame the PCM 1 but the fact that only one speaker is affected and that it happens when the unit is turned off suggests that's unlikely to be the cause.

The sound and the regularity of the timing suggest to me that it may be some odd capacitance issue whereby a cap is charging and when the charge reaches a fixed level after five minutes it discharges through that speaker. But that cap could be an electronic component or it could be something non-electronic acting as a cap and building a static charge perhaps due to something rubbing against it.

But that's just a bit of hypothesising and gets me no closer to an answer. What I'm really hoping is that someone out there has had the same fault before and managed to isolate the cause, or that someone with greater knowledge than I have can suggest further diagnostic tests to try and isolate the cause.

Here's hoping...