My 2004 GT has this air cavitation noise from the K&N intake between about 2000-3000 rpm. Between that and the three coil packs wining for the ignition, it sounds odd. I used to worry about it, but after putting 100k miles on the car, getting more power and/or fuel economy with this intake, I just ignore it now.
After the GM dexcool lawsuit, I changed out the dextcool and keep my overflow canister closer to the high mark. Upon moving from a standstill I hear it slosh around more now too. I figure this is just making sure the car works the way I want even if it sounds worse.