If it was a 205 or fester or escy I'd say pedal box, but I haven't got my hands dirty on my
Ibiza yet... Does sound like a possibility though.
On pugs, there's a bolt through the frame that the pedal pivots on, if it works loose you can get a similar sound.
Either way, check it out. If your pedal box goes on you all of a sudden you can't drive very well... and if you were driving hard it could be extremely dangerous!