I was trying to record some drums using Garage Band on my MacBook Pro. I have a microphone going into an amp and then the output of the amp goes into my computer. The amp is there to provide power for the mic. I've done this before and I've had no problems. However I was doing a test run before I actually started recording and I recorded about a 10 second-long test audio. About 3 seconds of this worked fine but then something happened to the feed. It started having this pulsating effect on the recording. It kind of sounds like I'm removing the mic and reinserting it over and over. Since this started happening, this is all my mic input on my computer does. I've looked at the audio options in System Preferences and it is the input not Garage Band. Also I tried plugging in headphones into the input jack just to see what would happen and I get the same pulsing deal. Does anyone know how I can fix this? It seems to me that it is a problem with my jack but I'm not sure. Thanks alot