noisy input when recording

Just bought a new windows 7 computer. Dell 15r 8 gig/ram, and i5 processor. downloaded audacity and about half the time i start up the program i have what seems to be an overdriving input from my usb microphone. high grass level and any audio input is off the scale. other times its fine. my old computer doesnt do this so its not the mic and ive replaced the cable. im wondering if a setting changes at times when audacity opens.

VOIP programs such as Skype will often change the audio settings (without telling you).