Camtasia for Mac is compatible with numerous audio sampling rates. However, under some circumstances, sampling rates such as 48000 Hz or 96000 Hz may not work properly and may result in noisy or distorted audio. This problem can occur with both Camtasia recordings and imported media containing audio. Camtasia generally works best with audio that has a sampling rate of 11025 Hz, 22050 Hz, or 44100 Hz.
Application programs on OS X can set the sampling rate and may have changed it to a problematic rate. Mac OS X has a program called Audio MIDI Setup, located in the Utilities folder inside Applications, which can reset that sampling rate for input and output. Open Audio MIDI Setup and make sure the Input and Output Format are both set to one of the above listed sampling rates.
Imported media with a problematic sampling rate can be converted to work correctly. See this article for information on converter software for the Mac platform.