I have 2 Hartke 410 XL cabinets that I bought new back in the late 80's (with the "Transient Attack" badges). They have been sitting unplayed since at least the mid 90's. They were in a bedroom, so they were not exposed to any temperature or moisture extremes. I figure it's about time to sell them, so I plugged them in to see how they sound. One of them sounds fine, but the other has an issue. The sound is clear on attack, but if you sustain a note, a subtle hiss or distortion can be heard. The noise is not constant, it comes and goes, and sometimes crackles a bit. I'm not very well versed on the technical side of amps, speakers, and such, so any suggestions of what's happening (or might be happening) to cause this would be appreciated. The cabinet has never been opened or speakers removed. Thanks!