Weird crackling from speakers when preamp connected

I had it looked at by a professional, they ran tests & checked the tubes, no issues when they had it hooked up and couldn't reproduce the issue. I haven't tried to clean the terminals, but may give that a shot.

That has got to be frustrating. 

Perhaps it needs to go off to VTL.

I remember giving a tape deck to a professional electronics repair a long time ago and having it never sound good again. They can be good for replacing and capacitor or resister... but sometimes not for nuanced stuff. VTL, shoud  have an engineer that knows were something like that can happen and find and fix it. Hopefully 

I’d be going back to that service guy and politely ask WTF???  It was working before he got it and doesn’t work fine when you got it back.  Pretty damn simple math there, and I’d be right pissed off if I was you. 

+1 @soix 

I would contact VTL and also try to talk to the person that actually worked on your preamp. 

If there were new parts involved, perhaps find out if the replacement parts were the same specifications, the same manufacturer and that they were new.

The service person and I talked extensively about the preamp, he ran tests on the device, tested tubes, no parts were replaced. They also hooked it up to a system and couldn't reproduce the issue.

Again it doesn't happen when I run my DAC directly to the amp, only when the pre is in the chain.