High revs and whistling
SEAT LEON ST Box Body / Estate (5F8)

Hello. Before I go to a garage I wanted to know what maybe the issue. 

I’m having occasional whistling noise from front of car when it’s accelerating to change gear. It is an auto. 

Also when start up from cold, most the time it starts at high revs at 1.2 rpm and then slowly works it way down to 0.7 which is the usual it sounds very loud and also makes this whistling noise and takes about a minute to go down. However when I turn off the ignition and start again the noise doesn’t happen. 

Really unsure as I don’t want this to be an expensive fix and wondered what may be the issue. 

Thanks in advance.