Sorry, that's the best I could describe the noise. (I searched, nothing came up that was similar to mine's)

And it only happens during cold start ups too, like when I get in to go to work in the morning. I'll get in, press the clutch in, turn the ignition knob, and a subtle "thump" sound coming from the engine bay area. But when the car's warmed up and started again, I don't hear it again until the next morning. Weird.

Any clues?

 

Okay after some more extensive searching, it's probably the rear diff pump turning on?

I just had the ACD pump replaced under warranty a month back, but I swear I noticed the noise before then too. They also did the 30k mile service while they were in there too.