VW Golf TDI makes a 'sneezing' sound on startup

Question

I really don't know how else to describe it. Car has no issues starting or running, but for about the last 2 months every time I cold start it, the engine makes a sharp, high-pitched noise like a sneeze.

Can anyone tell me what this is or why it's happening?

UPDATE:

Ok, I finally managed to record the noise. I realised in my attempts to record that it certainly does not happen "every time". It happens maybe one time in ten, and rarely on a cold start. More often than not, it happens after I've been driving for a while and then stop and start the engine.

Here's the link to the video. You can clearly hear the squawk just after it starts.

http://www.youtube.com/watch?v=UlqBFf63wXE

Answer 1

We have a Mk4 TDI Jetta that makes a sound after startup that might be described as a sneeze. I'm fairly confident that it's the starter motor's overrun clutch.

As soon as the engine "starts," it begins turning faster than the starter can turn. For this reason, starters have a one-way clutch, called an overrun or sprag clutch. This permits the starter to turn the engine, but prevents the engine from turning the starter, protecting the starter.

On my vehicle, I imagine there's some play or a worn bearing in this clutch, because as soon as the engine fires, there's a short (~1-2sec) buzzing noise that starts high in pitch and decreases in pitch quickly as the sound dies away. One might desribe this sound as "throat clearing" or "sneezing" in nature.

Answer 2

This is a noise typical to Volkswagens. It is the starter motor. The starter motor extends into the bell housing of the gearbox. The extension on the starter acts as a support for the front of the starter motor. It runs in a bushing which becomes dry over time. You can either ignore it, or remove the starter motor and with a long artists brush and put copper based grease into the bush, then refit the starter. The noise is the starter slowing down and chattering in the bush.