I installed my injen intake a couple of weeks ago. I love the looks of the intake. It sounds very nice but there is an annoying whistle when I tap the gas while crusing. Basically, it almost sounds like brake squealing.
This happens whenever I give it throttle at any rpms. Is this normal?

 

Yup, that hissing is normal. Kinda sounds like a blow-off valve.

 

I concur, its normal.