Loud buzzing noise on cold startup - A4 Cabriolet 1.8T

[markae]

Hi,

Can anyone help me to diagnose the following problem:

I have an A4 Cabriolet 1.8T (2004). Related or not, I have noticed over the last couple of months that when I start the car up in the morning the exhaust sounds like it has a hole in it but it goes away after a minute or so and its fine for the rest of the day. More concerning is that over the last week - and only when I start up first thing in the morning (it's fine even after leaving it throughout the day) - there is a loud buzzing noise when I start up. I opened the bonnet to try and locate the sound and it appears to be around the fan area but its hard to say.

The buzzing noise only stays for about a minute (or less) and then it sounds normal.

I'm obviously concerned it could become more serious if I leave it (other than having a nasty sound at startup which is annoying).

After doing some research on the Internet there seems to be related problems to batteries, alternators and exhausts. Has anyone got an idea what this might be?

Cheers,

Mark

[blackpool1974]

The high pitch noise from the engine bay is normal, I have a 1.8T A4, I think its the ECU checking all the electrical connections including ABS. It clicks when it is finished.

It happens as soon as you turn the key, before you crank the engine

[bez101]

i dont think the noises the 2 of you decribe are normal iv had around 12 b5 b6 b7 iv never had any of those noises i own a b7 and a b6 at the min apart from the clicks they dont all make loud noises buzzing or high pitched
just the normal clicks

[markae]

It's only just started doing it so I am comparing it to what it was like before (which I guess was normal!).