Hmmm... I wonder if maybe a pulley is off balance. You said it was just at idle right? Is it present when youve applied a load (heh) to the engine (push the throttle button)in park/neutral?

Have you tried pulling codes? You get codes with no CEL quiet often.

I can only hear it at idle inside the car with the windows up.

Really? I'll hookup my scan tool when I get home from work to see if it shows anything. I'll just keep it in the car with me so maybe I can pull up something before disconnecting the battery when the car doesn't want to start. Hopefully I can find something. If I don't see anything, I'll probably start off by getting a new cts. I read that it has a lot to do with telling the ecu how much fuel to let through and when it starts to go bad, it can cause all kinds of problems.

Yes really, a CEL only means your vehicle's computer has determined that a component or system in your emission control system is not working properly. So you can have other issues outside of parts effecting emissions that effect the motor and how the car runs.

Ok thanks. So even if I have a cheap scan tool, it can still read other codes even if the cel isn't on?

A cheap scan tool should be able to read all engine codes with out a CEL it may not read airbag codes abs codes alarm codes ect though.

On my CQ you read codes by shoving a resistor connected to a led into the OBD port and counting flashes!

Ok. One more question. Where is the crankshaft position sensor located and is it hard to get to?

I have a new cts ready to install tomorrow. I'll check for any codes first and will post the results tomorrow.

Well, it didn't pick up any codes. I put in the new cts and the car started up right away so I guess we'll have to wait and find out