effects/inserts causing distortion

When I go through my interface clean my guitar sounds fine when I add any type of inserts/effects such as the vst amp rack and monitor the sound it becomes very distorted and loud without even playing anything. I am using headphones so it does not have to do with my proximity to speakers/cab etc… my guitar is fine, it either has to do with my interface (fast track pro) or more likely a problem in cubase 6 but I cant be sure. any information would be greatly appreciated, and as always thank you in advance for the replies - MIke.

Could you clarify your description a bit? You know the VST amp rack generates distortion, since its an amp sim right?

“it becomes very distorted”

What becomes very distorted?

I assume you’re putting the amp rack on a guitar track as an insert. Are you saying that the entire mix then distorts? What happens if you take out the amp rack and put a compressor in the same spot? Same distortion? Different?

Are you hearing a buzzing sound perhaps when nothing is playing (neither your track nor your guitar)? That’s kind of the nature of plugging a guitar into a high-gain amp, either virtual or real, though there might be some ways to minimize it.

increase the sound cards buffer size.