Doesnt sound like it would be a normal noise mate. I can honestly say mine doesnt make a noise like that at all, and if dealer is prepared to do work on it then its obviously something that'w wrong.
Keep pestering. My only extra advice would be to make sure you keep documenting everything.
Phone call date and times, who you spoke to, and what was said.
A diary of sorts.
Sound and video of car pre and post work (preferably time stamped) will also come in handy.
If you have another issue being dealt with as well, treat that in the same manner.
You've bought a new car and there are certain expectations that a consumer should be able to rely on.
A car 12 months old and 4000km on the clock shouldnt be doing this.
Keep hounding them. Keep professional. And keep all records.
The fact that they've already tried to rectify the problem tells me that there IS a problem and its not just imagined. I bet they took you much more seriously when you showed them an audio recording of it!
They were probably hoping you'd just disappear
.