Is that a mechanical buzz (from the amp) or an electrical buzz (coming out of the speakers)?
In either case, something is probably loose... Something could be loose mechanically or electrically. i.e. It could be a loose screw/washer (some vibration is normal from the AC transformer), or a loose grounding-screw, or loose connector, etc. If you have to take the cover off to wiggle things around and push on things, etc., it's worth a try. If it's an electrical issue, just unplugging and reconnecting the internal connectors might cure it. I'd leave the power on when wiggling/pushing things (so you can potentially zero-in on the problem), but turn it off before disconnecting/reconnecting connectors. (And be careful of the AC power.)
...I once had a VCR the only worked with the cover off. I never could find the problem because it just wouldn't fail with the cover off. The repair shop gave-up too. (That was back when VCRs were worth repairing.)
In either case, something is probably loose... Something could be loose mechanically or electrically. i.e. It could be a loose screw/washer (some vibration is normal from the AC transformer), or a loose grounding-screw, or loose connector, etc. If you have to take the cover off to wiggle things around and push on things, etc., it's worth a try. If it's an electrical issue, just unplugging and reconnecting the internal connectors might cure it. I'd leave the power on when wiggling/pushing things (so you can potentially zero-in on the problem), but turn it off before disconnecting/reconnecting connectors. (And be careful of the AC power.)
...I once had a VCR the only worked with the cover off. I never could find the problem because it just wouldn't fail with the cover off. The repair shop gave-up too. (That was back when VCRs were worth repairing.)