My Subaru WRX has been making a strange noise for the last 5000 miles or so (it may have done it before that, but that's the first I remember):
When I pull away in first, or sometimes if I just rev the engine when stationary, there is a distinct noise of flowing liquid, like slush pouring from a bucket, coming from just about where the gear stick is.
My assumption is that it is oil lubricating the gearbox, however I have never heard it in any other car so it seems weird to me. My next service isn't for a couple of months but if this is not good I'll book it in sooner.
I don't notice any problems - changing gear is as slick as ever, there are no clunky shifts.
After paying a lot more attention to the noise, which is a challenge as it is intermittent, it does happen when revving and pulling away, as well as revving with car in gear and the clutch in or in neutral with the clutch out.