I recently bought an '04 SVTF, that the PO had installed a short ram intake on, it whistles like crazy. I have found through light application of the gas while driving ( I have a sensitive foot and can keep it at one spot for a while, a result not having cruise control for 8+ years.) I can get the throttle open to just enough where that's all I hear is a light, consistent whistle.
I can tell you from experience that on my AEM CAI from my original SVT, you could also hear a slight whistle at partial throttle, but it was more prevalent if you floored it in say 4th around 30mph. You could really here the intake suckin hard.
I'm pretty sure the whistle you are hearing is a normal side effect of having the SRI on your car. Shouldn't be alarmed about it unless you start hearing abnormal whistling.
Current love affair: 2004 SVTF #953 (Josephina - pronounced hoe-se-fin-a)
RIP: 2002 SVTF #2358, Sent to graveyard on June 11, 2013. I will always remember the good times we had!!
This car made my hair go gray, and did not care.