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If the hum stops when you touch the strings or the bridge of the guitar, it's likely you've lost the bridge ground on your guitar. There should be a wire from the electronics cavity to the bridge to ground it. Check that it is well connected. It may require removing the bridge. This is more common on guitars with painted or powder coated bridges. You may need to scrape away some of the paint under the bridge so that the bridge makes a better connection to the wire. It's also possible it just came loose from whatever it was soldered to inside the cavity. If you want to verify that it's the guitar, get a hold of another guitar and try it on your amp.