Did anyone manage to ``repare'' a buzz, ever?

I have a buzz in my pream. Not a hum (I can cut it off when
I use the 80hz subwoofer crossover). I tried everything known to man to fight it externally (grounds loops, line conditioners, all kind of connections, nightlights, etc.). I strongly believe now that it is an internal problem. I wonder if anyone had experience with any kind of gear with the repare of such ``buzz'' problem. Is it possible to repare and/or worth it? What can cause it internally? Thanks in advance.