I have a Yamaha A-25 amplifier connected to Polk RT8 speakers. I have an mp3 connected to the AUX input. I noticed a crackling coming out of the left speakers tweeter and the tweeter audio sounds muffled. The crackling gets louder as the volume is turned up. I switched the speaker cables and the crackling changes to the other speaker. This makes me think that the amplifier is the issue. There are A and B speaker outputs; the crackling happens on both. What could cause this problem and can it be fixed?