This is almost always a mis-match between the setting in Audition (Edit/Preferences/Audio Hardware) and the Windows Audio Control panel.
Check the settings for Audio Sample rate on the Audition Preferences screen. Then go to the Windows Audio Control--you can get there either via the Control Panel or just right clicking the little loudspeaker icon in the bottom right of your screen then selecting Playback Devices. Once there, first check that the sound device you want to use is selected as the default with a green "tick" mark--I assume this'll be the built in sound card on your computer. Then right click on that device and select "Advanced" from the tab at the top. There'll be a drop down menu for "Default Format". Make sure the sample rate in this box is the same as the setting in Audition.
A couple of notes: some programmes you may run will actually change the default without telling you so you have to watch for this. Also, from memory the default setting in Windows comes as 48 kHz while most music recordings are 44.1.
Hope this helps.