Krell 707 problem need help

Hi. I am seeking some help regarding the Krell 707 processor. 

Lately, after some playing time - a started coming out of the speakers.  If I turned the 707 off and on again - the noise was gone, but returned later.  

Then one day, this rush became a loud screech, after which both amps (Krell) shut down. It sounded like an explosion. 

Now, an interesting thing: this phenomenon did not occur in either XLR or SPDIF inputs! Only in RCA. 

I contacted Krell and their response was: send it to factory. Alas, I live abroad so it is out of the question.  

A local technician who checked the machine didn't find any malfunction. He suspected some DC leak somewhere but warned it could cost a fortune to locate it.  

So my question is: has anybody here ever encountered such a problem in Krell or even more generally? And if so - were you able to solve it without shipping the amp to the manufacturer?

I would appreciate any input. 

Thanks.