squaling sound from vents???

[neilsv6]

hey,
the other day i was driving and doin 120kh and i startd to here like a sqweel coming from my front dimister vents it havs never done this till now...
COuld any1 give me ideas wat it could be???
and how to fix it
thanx

[Trent L]

If you were on a slight uphill grade, it is probably a vacuum issue.

There is already a similar thread about this type of issue:-

Calais climate control on 'AUTO' throws to demister when uphill grade ?? vacuum issue