Is SW 4 the one that gets extended? Codes would never approve this setup. Also, it could null and void your homeowners insurance. The buzzing is from bleeding amps as switch #2 needs to be a double throw and not a single.
If you insist on this set up use your meter to test continuity through #4 to 1-2 and 3.
The grounds serve no purpose with today's switches and plugs. Remember every foot of wire you lose 2% of your available amps-and every switch you lose 4%. Your meter should isolate the issue.