When I switched to Phono on Beomaster 5000 this evening, there was a loud hum in left channel only, the right channel is dead quiet. Then I switched sockets, again same thing but this time left channel output was thru right speaker and right channel output was thru left speaker, meaning that the left  RCA socket has the problem. I disconnected all other component to see if it will go away, it did not. When I touch the RCA cable or the RCA left socket, the hum goes away.

Again the hum is with Phono input only, all other inputs are fine.

Any ideas what could be the problem here?

Cheers  

Most likely broken PCB tracks and cracked solder joints at the RCA sockets.
It's very common.

Martin

My first RX 2 had the same problem about 20 years ago.  My (non-B&O) dealer fixed it under their free extended warranty, and it's been running flawlessly ever since.

Hi Rich, The turntable is indeed RX-2,  I should mention this, not only there is a loud hum in left channel, there is no music sound either, right channel plays fine without any hum.