when i first turn my heat on, weather the engine is cold or has been running for a while the heat makes a very strange sound from under the hood, i cant hear it very well inside the car but outside its pretty loud. i am trying to figure out how to spell the sound i am hearing but its not easy. i had my uncle listen to it and he said that it sounds like their are bearings that have grease around them but the grease is jelled up when cold and it has to be on for a while for the grease to to do its job. also the noise comes in intervals on then off on then off, it reminds me of the clutch on the AC kicking on and off. any ideas?