4 Wheel Drive/SUVs: noise, air conditioner compressor, fan clutch

Question
Hi I have a question about a 2000 kia sportage 4x4. The car makes a nose coming from the front. I do not know exactly where , it seems to come from under the hood. It happens more often when the weather is warm or the car has been running for a while .or when it has been running for a while and then you stop for example in a toll booth and when trying to leave. Sometimes in the highway the car runs perfect and if I stop in a toll or something when I try to go again the noise starts. It does the noise when stuck in heavy traffic and moving very slow also. I noticed that it does the noise also when the weather is hot and the car is being sitting there let's say overnight. I noticed it less in winter time , but it happens also. The first time I heard the noise I was in the highway and I thought that a truck was driving next to me since it sounded like the engine of a truck when is going in low gear in the highway .It is difficult to describe , but the car doesn't run as smooth as when the noise is not present, the transmission shifts well anyway, the truck does not overheats ever, but seems to lose some power , not much , but some. I already changed the water pump and nothing, then I changed the fan clutch and nothing . somebody suggested that could be the air conditioner compressor since the belt runs through the part even when the a/c is not in use and the engine is running. could that be? The a/c runs fine , not super cool ,but blows. I didn't think it was the transmission since the noise is there when the car is started in the morning sometimes. It is annoying and people looks at the car when I passed sometimes since it sounds like I am stuck in 1st gear and trying to force the engine , but the transmission is changing  fine, Could this come fromthe transmission anyway? are ther any other parts connecting engine and transmission or hoses, wires, cable s , swithches that would do this? I noticed it that in places like Jersey where there are lots of hills the noise starts more easily . Any suggestions beside going to a Kia dealer?

Answer
Claudio,

Some of the later model cars have an auxiliary electric cooling fan for use when the temperature exceeds the cooling range of the clutch driven fan and also when the air conditioning is on.if you turn the A/C on the noise probably starts hot or cold out or does it? If the auxiliary fan has a broken blade or is warped it will sound like a train running. Look on the front and directly in front of the clutch fan and see if there is another electric fan mounted to the radiator, this may be your problem

Matt