vcds output tests help?

[Vwdan80]

hi all, i was messing around with vcds and was doing the output tests in the engine part on my s3 and on the first test it is EVAP purge valve (N80). when i selected this i could hear a loud hissing noise from under the inlet manifold, so i'm not too sure if this is normal or if there could be a vac leak/problem??

The car runs ok and there isnt any fault codes at all,
any help would be mucho appreciated
Dan