My stereo is haunted!!

Hello Audiogoners,

I’m looking for some serious sleuthing. I cannot figure out what’s going on with my system. 

The basic system is:

• Bel Canto Ref1000M Class D mono blocks
• Modwright SWL 9.0 Anniversary Edition preamp
• Bel Canto DAC 3
• Either my old Rotel CD player or Cambridge transport to DAC
• GoldenEar Triton One speakers

I liked the sound. It was just fine. Then, out of the blue, when I started the system, I’d get static that would build up until I got a loud POP out of the right speaker. How loud? My dog is now afraid of my stereo. Well, she’s not that brave…

I have tried:

• Swapping in various tubes in the preamp.
• Sending the preamp back to Modwright for a full exam. Done for only the cost of postage- great company. 
• Switching the channels used for each mono block. 
• Switching the channel for each speaker. 
• Switching out the electronics in one of my speakers (parts supplied for free from GoldenEar- great company).
• Switched in Adcom GFA555
• Switched in a Dynaco PAS 3 Series II preamp
• Used all combinations of preamp/amps
• Switched out all cabling including speaker wire
• Added a Furman PL-8C to stop line noise
• Tried a different circuit in my apartment
• Tried powering off flatscreen TV, Roku, and WiFi router
• Switched between CD transports and used the Rotel built in DAC to take the DAC out of the system
• Tried new surge protectors and power line.
• Tried some medium sized Klipsch speakers I had around.

Nothing has worked. Some things (like the Furman, oddly enough) have added additional hum. 

I’m fine with basic tube noise floor. Not so fine with small booms and hum.  

I’m ready to go back to my Victrola and give up on electronics all together!

Guesses? Things to try? Have a problem like this before? Thanks for any clues!