Odd behaviour on initial cold start

[enc]

2012, A3, 1.4 tfsi 8v. Only  On initial cold start, 9 times out of 10, my car makes an odd whine/ whirring sound immediately following the engine firing this last for a second only( sods law it didn’t do it as I prepared to record it this morning) possibly the starter  running on after the engine has fired?  This does not occur on subsequent starts after initial cold start, even imefialty after switching the engine off and starting it for a second time. Also, when this occurs the engine revs are at 1200rpm! if an attempt is made to drive  in this state, there is hesitation in acceleration  and a slight turbo whine can be heard. This lasts for around a minute before revs drop to their usual  750rpm. The Car runs fine at this point. 

If the engine is immediately switched off and restarted after the initial cold start issue,  revs are at 750ish and the car performs normally. 

Unsure if the two issues are connected? 

Obviously, there is some kind of cold start system which I think should elevate the rpm on a cold engine!? but as said, when the idle is at 1200 rpm progress is poor. 
 

any ideas fellas? P

Edited August 7 by enc

[cliffcoggin]

Possibly the alternator belt is slipping.

[enc]

19 hours ago, cliffcoggin said:

Possibly the alternator belt is slipping.

Hmm, not that kind of sound cliff. I’m trying to capture the audio and I’ll post here.