I have an 04 baseline TL with strange chirping noise coming from the Engine. This only occurs when I drive it and accelerate it and it revs around 1800rpm. The sound is clearer outside the car then it is inside. Driving the car seems to be ok, I don't feel anything wrong, except the noise. This does not occur when the car is stationary and neutral and I rev it up to the same rpm though... I took it to a mechanic and he thinks the problem is the alternator, but so far people online who had similar problems seems to suggest areas around the belts...

 

I would think belts, had a similar issue in my old car, but never looked into it. Car drove fine and the sound wasn't always there.

 

Look into the small pulleys on the engine,bearings might be bad...my friend has the similar issue as you...and it was that

Easy way to check,get a long screw driver,press up against it as its running,put ure ear on the handle of the screwdriver,you should hear the clicking.

Two of them were bad in his 04 tl

 

Could be the O-ring whine. Could be due to being cold. Could be the Cold air intake. Mine has this whistle whineish sound.

 

I don't think it's the cold as it is freakin hot right now.

Couldn't find a screw driver, so I used a frying pan, didn't hear anything and got yelled at by the birthgiver. Thanks for the advice though.