Manley Amp is humming - troubleshoot :(

Hello all ...I have been chasing a gremlin on the left side of my system for about a year . Last night my Left side was completely distorted at lower volume and after that just turned into loud humming....

Manley Snappers
Manley Jumbo Shrimp Pre amp
Klark Teknik DN360 EQ
Source was Macbook Pro

So i switched the amps to see if the hum would follow the amp & it did ....even with everything off except amp... super loud low end hum ...like a grounding issue...changed all tubes 3 times , still hums ...any clues before I send it in?

thanks !