Mine normally whistles during acceleration, which I am pretty certain is the intake (and it definitely comes from that area). I'm running stock, with no aftermarket air filter, supercharger or anything like that. It also has nothing to do with outside temperature. I've heard the same thing while driving my mom's 3000GT, and it does sound a little bit like a jet engine warming up. I like it and assume it's totally normal. My roof rack used to whistle some but now if it did I wouldn't hear it over the tire whine, let alone the PV2. :-)