Question about performance and use of speech recognition on Vista

Hi:

I have a question regarding the use of Speech Recognition and what
performance hits I might be taking, if any.

I am not running Speech Recognition for that purpose - it appears that
my new laptop causes a high pitch noise any time the power supply
charges the battery. But, if I place the Speech Recognition system
into the middle option - not on, not off - but waiting for me to say
"Start Listening", the annoying high pitch noise stays off.

I cannot find any other permanent way to stop this high pitch noise -
see below.

So, what kind of hit am I taking for having the system always
listening for "Start Listening"?

Thanks,

Dave

PS - any other thoughts on how to kill this high pitch? The screen can
go into 'monitor off' mode per the Power Options Properties, and the
noise continues, so I don't think it is coming from the monitor. The
speaker system for the laptop is along the back of the keyboard, not
at the front, and the power input is on the side, right next to the
right speaker. Also, if I open the audio properties, and select the
Recoding tab, and then highlight the laptop's internal microphone
listed there, the noise also goes away. But, closing the Audio
Properties, or selecting the other tabs on that dialog brings the
noise back. Muting or turning down the volume has no effect on the
noise.