I have a pair of Polk RTA 8T where one gives out a muffled sound. I believe the mid-range, located on the very top is partially working but tweeter and sub-woofer is getting no power to it. Physically, they have no damage and appear to be in perfect condition. I suspect that there's a problem with the component that interfaces with the speaker wires (amplifier?), where the coil or one of electrical parts (perhaps a capacitor) went bad. Any thoughts?