Quiet Speakers on my '99 Avalon

I've got a '99 Avalon XLS and the speakers got really quiet one day. Even if you turn the radio all the way up its super quiet and you occasionally hear crackles from the front. I thought they were blown and bought new 4 in speakers and when I put them in and there was no difference. I've checked the amp as well as the radio wiring and both seem fine. Please help.