I always thought that was generally caused by a bad ground in the system.

 

I spent yesterday installing my new sirius s50 and noticed the whine when using the aux input. I'm taking the s50 back to bestbuy today becuase when I start the car I loose my antenna signal. So there is something going on with the Aux input and the whine. If it's bad I'll switch to the fm transmitter. I'll be replacing the stock radio in the next few months anyway if this is a permanent problem with the HHR radio.

Ng

 

If you are still having problems with it ,here is another option, you can check with radio shack, for a noise gate or noise filter,years ago nearly all car stereos would pick up ignition noise and this little filter would remedy this known problem.

 

you can go to radio shack and see if they have a ground loop isolator and wire it in they work good and as far as the wining it is a bad or not a good ground