If your not sure whats going on with your BOV,
FLuter doubts, Leaking doubts, testing the best vacum line etc.
Heres something Ive had good luck with.

Go to a toy shop and ask to see their whistels. They come in all shapes and sizes.
You have the ball type and the wheezer type, farting type etc which are put into ballons. Buy at least two. One that will sound with very low pressure like the ballon type and one which will sound with lotsa pressure big ball type.
Stuf them into a hoze and clamp down. If required use some duct tape.

Now even the slightest air out of the Bov can be heard.
Besides which youll be the first guy with a Farting Bov on the Block.
Pics if your intrested.