The original AC30 chassis design is a scary looking thing. The circuit itself is also not well designed from a noise standpoint. Many of the grounds that make the amp work rely simply on the connection from one chassis section to another ( the chassis is made in sections and they bolt together ). They didn't veer far from the original design much in the newer reissues, so many of the grounding issues, as well as some created by the PCB design, created issues. They attempted some band-aides in subsequent revisions, but none completely solved the issues.
There is an amp tech on YouTube called Psionic Audio that specializes ( at least seemingly ) in Vox amps. He goes through great detail and lengths to describe and prescribe how to fix the buzz issues among other things in the AC series amps. As I said, I am not a fan of the AC30 circuit, and while it does work very well for some people, in the perhaps hundred or more I have come across, only a few have been desirable to my ear. Not sure which channel of the amp is the most popular? I figured it was the top-boost channel, but the most famous users of the amp use the normal channel, the top boost channel is so bright I would rather chew glass than listen to it.