I have owned a ampeg tube amp and two crate speaker cabinets for a few years now and have played at extremely loud volumes in heavy metal bands. As far back as I can remember, the tweeters in the cabinets make a loud buzzing sound when I take my hands off my bass strings. It sounds like popcorn. I am not sure of the model of my crate cabs, but the one on top has 2 10"s and a tweeter and the one on bottom has 4 10"s and a tweeter. They both have a switch in the back that says "high frequency attenuator." The settings of the switch are "off", "-6", and "0". The popcorn sounds only happen on settings "-6" and "0". It sounds worse on "0". I am assuming that when it is on "off," it turns off the tweeters. However, the tone of the bass sounds best when they are on "0." The noise only happens when I take my hands off the strings. Does this mean the tweeters are blown? if not, what could be wrong?