Levinson 390s -- intermittant loud cracking sound

What type of speakers? Are they ES or powered in anyway?

Montana EPX. Not powered. I did a lot of cable switching tonight to see if the noise jumped to the other channel. I also found two of the fuses on my right BAT VK150 monoblock blown. I'm now trying to figure out if it's an amazing coincidence that the amp happened to have an issue (tube? --- they're not that old) the same time I intro'd the 390? Or, did the noise that initiated at the 390 create enough of a pop / spike that it was the root cause of the blown fuses? I replaced the fuses, switched the XLR's out of the 390 to see if it jumped sides. I heard no further pops. Switched them back to normal and have still not heard anything. Not sure if it was bad cable connection? Seems unlikely, but I guess it could have been dust or contact issues on the connector of the 390? I bought it from original owner who said he has perhaps 40-50 hours on it at most, and it has been disconnected for some time now (he's now into High Res digital audio). I'm not sure what caused it. And I'm not positive if it's gone for good? Any input is appreciated. Thanks.

Is this the first balanced connection in your system? I have a 36S and one channel quit. The Mark Levinson service center put it back in top shape. They also replaced all the caps which I gather get old over time regardless of use. Mine now sounds great.

after much cable swapping to isolate the issue, I concluded it is indeed inside the 390 or the XLR connector on the back. returned the unit. thx.

A loud transient can blow the fuses on the BAT 6C33C output tubes. However once those tubes experience that condition they may arc out repeatedly. After several such instances the tubes should be replaced.