cold start jet engine noise

During a recent cold snap after starting the engine, I heard somethig electric rev up quite a bit, only to wind down after about 15 seconds. This is not the normal RPM adjust... this sounds like an electric motor. Any ideas?

I had the same problem on startup, it eventually progreesed to happen all the time, it sounded like a shop-vac was switched on when you step on the gas, very annoying. It was the fan clutch. Apparetnly the electronic sensor that contols the clutch failed. When the sensor fails, the fan eventually stops spinning. The noise is appatently something in the clutch. Unfortunately you have to buy the whole assembly. you cant buy just the sensor, the cost is $300 for a GM part, maybe less for an aftermarket part. I had mine replaced with a GM part and the engine has never been so quiet.

I also noticed this on mine when the outside temperature gets down to around 0. This morning it was about 30 degrees and it didnt do it.