Click on "Navigation" (Right side of the console)
Select "Features" (Left side of the console)
Select "Real-Time Scanning"
Under settings scroll down to the section "check removable media drives"
Select the option "When I Plug in a drive, ask me to scan it" and Click "Apply"
This should allow you to decide if you want to scan external/removable media when it’s connected to the computer.
For improving the PC performance during the scan. Scroll down further under the same window and select one of the options that suits you under "Choose how thoroughly to scan my PC (Advanced)".
I appreciate your suggestion, Sanjay, but the setting was already marked "When I plug in a drive, ask me to scan it." I changed it to one of the other settings, clicked apply, then reset it to "...ask me..." and clicked apply again, but that did nothing to alter the situation. When I plug in a drive, McAfee does not ask if I want to scan it. It just goes ahead and scans eating up CPU. Any other suggestion?