I have had this issue before on my 2003 Polo, after installing coilovers and then doing a few thousand miles and now my A3 has developed it. As I'm pulling away from stationary (just as the clutch bites and the wheels start to pull the car along) I get a pop/ click noise which sounds like its coming from underneath the car somewhere, possibly footwell area or underneath the forward seating area. It is one click/clunk and thats it, until I stop and pull away again. It never happens at speed, just the initial load of pulling away and sometimes braking to a halt. I've checked all the wheel nuts and they're fine, so its not that (although it kind sounds like it did when I had some loose ones of my previous car!). I'm wondering if it is the chassis/subframe bolts not being tight enough and allowing some very slight movement when the chassis is placed under strain when pulling away... maybe? Anyone else experienced this at all? I have heard the MK5 Golf lads complain of similar issue on lowered cars! Its definitely chassis/subframe suspension related I'm sure of that.