Stereo & Electronics - Door Speaker Problem

I have a 98 Trans Am with the stock Monsoon system and speakers. A few days ago my drivers side door speaker went out. It turns out that when the tweeter plug is connected, the main speaker doesn't work. If I unplug the tweeter, the main speaker comes back on, but there's a chirping noise like a cricket. The crickets are worse when I'm playing through my iPhone via the iSimple kit plugged into the CD Changer connection. It's pretty irritating, so I left the speakers unplugged.

Anyone know what's going on here?

Thanks.

Q