My 2001 T5 has just recently started producing an audible high-frequency sound that can be heard mostly when outside of the car and that I have pinpointed to be coming from somewhere on the right side of the engine bay behind the intake box...I was thinking it could be a small leak in one of the vac lines...thoughts?

 

When it does it pull the dip stick and see if it stops. If so then it might be a vent box problem.

 

The oil dipstick?

 

Yes

 

I pulled the dipstick and the noise persisted. When you put your ear behind filter box the high frequency leak sound turns into a hissing leak sound...is the vacuum located in that region?

 

Check the hoses down by the turbo.

 

The car is at my dad's, so it will be him checking it out...is the turbo back behind the block?

 

If you follow the bog plastic hose from the air filter box towards the back of the engine it runs to the turbo.