I had this problem once too.... now perfect once again
Its linked to the starter motor, the problem is the little bush on the end of it - it gets worn away / cracked etc... and spins freely causing the wheezing noise
What you need to do, is remove the starter motor and replace this small and cheap bush and you will find the sound gone... can be bought from vw dealer parts ("bearing bush")
Personally I changed my starter motor for a new one at the same time, in case the slipping caused any internal damage to the starter motor etc...
Hope this helps!
The sound it makes can be very embarrasing !!
p.s search for posts about me on the subject for more info