For the past few months, I have noticed a strange noise coming from the 4AFE engine of my 1990 Corolla. This car has 75k on it. When the car is cold, the engine seems to run fine. Once driven for a few miles, it decides to play a song for me under the hood (when I stop) ... sounds like a saxaphone. My first guess, is that there is a vacuum line off or something controlled by the vac line, acting up. I've looked around and can't find any vac lines off or cracked. The engine runs pretty good, but this noise is driving me nuts. It's an automatic shift, if that helps any. Any ideas as to what is causing this noise?