I installed the Aircharger Kit about 2 weeks ago and notice a vacuum hissing... is this normal at idle or is a defect in the kit???

Well since K&N wont see this I will answer for you. The hissing you hear is actually a sucking sound as of the open air intake sucking in the air. Its perfectly normal. INfact your old intake box did it as well you just never noticed it before because it wasnt as loud.

Where did you purchase you K&N air in-take system and did you install it yourself? Do notice a big difference? Let me know?

I purchased it through a local performance shop. To get it cheaper though buy it online through www.4filters.com or at www.4x4parts.com they both sell it for like 220. yes i installed it myself took me about 45 minutes and yes i noticed an increase in power.