3 way switch problem

Even when removing black wire #2 from switch #2 problem stayed the same

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.

How 4-way switches work -- an animation

Sorry about that previous post. It was sent erroneously.

The reason switch 4 cannot turn off the light is because of the black wire coming to switch 2 from cable 2. With that wire connected there is no way for switch 4 to interrupt the power to cable 1 lamp.

Your flickering lamp and buzzing sound is most likely either a loose connection of the red wire on switch 2 or a defective switch 2.

Thank you All for replying, The problem was a loose connection, Everything works fine now.