This is the "free" 1973 cabinet a friend gave me. I replaced the speakers, and it still makes a bad noise when I play a low C on the E string. I think I know where the noise is coming from now. I used a freeze pedal and played the low C on the E string. That allowed me to investigate the noise hands free. I noticed it stopped when I applied pressure to the bottom of the top left speaker, but is also stopped when I applied pressure to the wood face between the top row and the next row down. It appears that the wood face and the top partition is loose and vibrates at and around low C on a four string. But how to fix it? I was thinking of putting a few screws through the face and into the partition. Is this too crude a fix for an old cabinet? Any suggestions would be appreciated! Before I replaced all the speakers with new ones, I wish I would have just bought a new cabinet!