Audio Input Problems, Short bursts of sound Options

[musicteacher]

I am not sure if this is a hardware or software problem. My iMac is only receiving external audio input in short, irregular bursts, insterspersed with no signal at all. I am running OS9.2 and trying to record using Cubasis. I am having this problem with both a Griffin iMic and my built-in external audio input jack. Any file already on the iMac that I import into the Cubasis arrangement I'm working on also only plays in short, irregular bursts even though they play fine in iTunes. Please assist. Thank you.