Buzzing in Speaker while Playing CDs

I have a Cambridge CXC CD transport connected to a Schiit MultiBit external DAC. Recently there developed a buzzing in the left-channel speaker ONLYwhen playing CDs. After a bit of sleuthing, I replaced the RCA cable from the transport to the DAC with a new optical cable. The problem was temporarily resolved. Several weeks later, the same buzzing reoccurred. This suggests to me that the cables between the transport & the DAC are not the issue; but rather the transport or the DAC. Since I do not have another transport nor another external DAC, I am at a loss in trying to isolate the source of the problem. Any suggestions that you might have would truly be appreciated. Thank you kindly.



As suggested, simply flipping the right and left RCA cables that connect your dac to your amplifier (or preamp) will immediately tell you the source of the problem.  If it stays in the left channel it's downstream (amp or speakers) and if it follows the cable then it's upstream (the cable itself, the dac, or your transport).  Super quick and easy to do, no need to clear the schedule for the day.  

Thank you so much for the response. Life has been busy lately. But as soon as I get back into town next week, the diagnosing will commence.

I finally had some time to work on diagnosing the problem of the buzzing. The first thing I did was to disconnect & clean all of the cables & verified that all of the connections were solid. With the help of my son-in-law we followed the suggestions offered here in the thread. We also connected another CD player to the "suspicious" DAC.

Unfortunately we could not get the buzzing to reoccur. At this point I don't know if the cause of the buzzing was associated with the cables/connections or possibly the dreaded intermittent electrical gremlin. So going forward  I can only wait for the buzzing to reoccur & then to connect the DAC to another CD player.