Chevy Venture noise from the engine

I have a 2001 Chevy Venture with 140K miles on it and over the past two months, I've noticed a medium pitch "turbine" type noise from the engine. This only occurs after I've been driving the car for about 10 miles. The pitch of the noise changes with the engine rpms, not the vehicle's speed. So if i take my foot off the gas, the noise goes away. But as I rev the engine higher, the pitch gets higher though the pitch is never very high. The noise does seem to be getting louder over time.



I bought this car used about 4 years ago and since I bought it, i've had the head gasket replaced because of a coolant leak and the AC system replaced, the bearings replaced and the brakes replaced.



Recently, I noticed that the car overheats at idle and there wasn't any obvious leak but the radiator was low while the resevoir was full. I changed the radiator cap and that seemed to fix that problem.



I was hoping that would fix the noise but it did not. I was thinking that maybe the water pump was making the noise since the pump is connected to the engine via the serpentine belt and engine rpms would affect the pump. I dont see any leaks at the pump and it seems to be spinning fine and when its at idle i can't localise the noise.



Anyone have any ideas?



Response:



It may be that your power steering pump resivior is low on fluid. Would be the first thing I would check. If all your fluids are good, then I would remove the belt to make certain the noise wasn't internal in the engine.



It is possible for it to be the water pump, but not as likely as it would be the power steering or the alternater going out. In my shop I use a stethescope(sp) type devise to listen in close for noises, the old timers used to use a long screw driver and touch it to part of the engine and the other to their ear..... some use a piece of garden hose.... you an try those at your own risk....