I very confused about my line in port. I'm trying to hook my macbook up to my 4 channel PA using a 1/8" input jack, im using garageband, but I get no response. the driver is switched to built in line in port but still nothing. I find that when I unplug it a little bit, the computer picks up the sound but there is a strange fuzz sound that accompanies it. so basically, the input does not work when I plug it in all the way. any ideas?? I know it worked before, perhaps I blew the input?