Hello guys. 
After driving 170 miles home yesterday I parked up for half an hour before popping to the shop. On my journey to the shop I became aware of a whistling engine noise even when idle. Next day nothing but only drove a few miles. The car has done 74k and had the cam belt & water pump  changed at 52k 2017.  Any ideas guys? Thanks. 
 

2012 Skoda Fabia estate 1.2 TDi greenline 

I'd look for a slight boost leak.

Where do I look for that please?

Between the turbo and the intercooler.

Have you got a video? There shouldn't be any boost at idle so I don't think it's intercooler piping related. Does the car feel slower at all?

I’ll try and do a video later when the roads are quiet but not heard it properly since that long journey on Tuesday. The only time I’ve noticed it seems slower is sometimes in first gear it take 2-3 seconds before it get a shove on like it’s lost power for a couple of seconds. Apart from that once it wakes up it goes well for a little 1.2 tdi.. It was 23.5 here today and I thought I could hear it again but the traffic and wind was very loud so not 100% sure. Whatever it is it’s not constant but random…🤔