Sorry if this has been covered, but I did a quick search first and didn't find anything.

I've noticed that after I've exited the vehicle, I'm hearing a high frequency oscillating tone or whine of some sort coming from my CTS, but I can't isolate where the sound is coming from. It only lasts for 10 seconds or so before switching off. Something to do with the HID's, maybe?

You're likely hearing the HDD. Sounds almost musical if you listen closely enough.

You're likely hearing the HDD. Sounds almost musical if you listen closely enough.

I don't think so. Besides, why would the HDD continue to spin after the ignition was turned off and I have exited the vehicle?

I hear it too, I don't have the HD and wonder if it has something to do with the LEDs or HIDs because I can only remember noticing it at night.

I don't think so. Besides, why would the HDD continue to spin after the ignition was turned off and I have exited the vehicle?

Well, one possibility is that if you're tuned to any radio station, it's going to keep recording for an hour even if you've turned off the ignition.

If someone doesn't have the HDD, then this isn't what's happening or something else is happening to them.

I suggested this because when I first got my car I wondered what the noise was and it turned out to be the HDD.

OP - do you have DI motor? I have heard that too and thought it may have something to do with the high pressure fuel system.
ABS? or the articulated headlites turning in?
rg

I was recording to the HDD from CDs while the car was in the garage. The entire time the accessory power was on, this high pitch whine/tone was there. This went on for many hours while I was loading up the HDD with music. The noise stopped a minute or so after I was finished.

It sounds like a DC/DC converter. There is possibility that some of the equipment uses higher voltage than 12V, hence the need for the converter. I am not sure but this is how it sounds to me....

I'm nearly positive that it isn't the HDD that I'm referring to, because I don't hear the sound inside the car, but rather when I'm standing outside of it - and only for several seconds. That point someone else made about only hearing it at night is correct, in my case, also. It seems lighting related, somehow, because I think it stops as soon as the LED's/HID cut off. No big thing. I was just curious. I do not have the DI engine, BTW.

monster :domo: lol

I wonder if the HIDs do their little thing when you turn the car off like they do when you turn it on..

When you get out of the car, run to the front and see if the HIDs do their little balancing dance :)

You could also try to listen for it when you start the car, but I'm not sure you'd hear them over the engine...

I'm pretty sure its your HIDs. I notice the same sound and it goes away when the lights go out.

Actually, believe it or not its the T43 TCM in the transmission. When we started development of the programming way back when and had one on the bench one person commented on the fact that it squealed like a pig when it was powered up depending on the calibration. Sure enough the second the TCM gets the "disable normal communications" message prior to programming and the unit begins programming the noise goes away immediately. I know, its crazy although maybe there ARE two different noises but on my car I can hear the TCM.

And yes I know this sounds crazy LOL :D

just had the engine running with the sound shield removed. shut it off and noticed this high pitched noise is obviously coming from under the hood. tcm it is.
rg

An easy way to check is, if the car has been sitting for awhile IE the bus is asleep walk up to it and hit the unlock button. That should turn the headlights on but not wake the rest of the bus up, you shouldnt hear it :)

this was covered about a 2 months ago---it is the hard drive winding down

Sorry if this has been covered, but I did a quick search first and didn't find anything.

I've noticed that after I've exited the vehicle, I'm hearing a high frequency oscillating tone or whine of some sort coming from my CTS, but I can't isolate where the sound is coming from. It only lasts for 10 seconds or so before switching off. Something to do with the HID's, maybe?

There have been earlier threads where HDD noise was speculated. the HDD is inside the car and I can barely hear it. The OP describes the sound heard from outside the vehicle, I have heard this after exiting so all doors and windows are closed. it is not the HDD.
open hood. close drivers door. open passenger door. turn on key. start audio recording. turn off key. RAP is active so audio continues to play and record. put face under hood. listen to whirring noise and some clicking. noises stop. a few seconds later HIDs go off. audio continues to play and record . . ..
end of thread.
rg

I only have three options on my '08 CTS. Leather Seats, Radio with the Hard Drive, and Automatic Transmission (yes, I know, but it really is an option). Anyway, I hear the same noises you all describe. I noticed that they are two different noises though. The HDD does make a little musical noise, almost like R2D2 from Star Wars. It is only audible from inside the car. The other noise is a more stable, high pitched tone, audible from outside the car. I believe this noise is comming from some electronic engine or transmission controls. Since our transmissions "learn" our driving styles, and based on some of the posts above, I find this very reasonable to believe that when shut down, the transmissions go through som element of "shut down procedure" much like any computer.