Hi Daniel - The NT is a super amp but it's not the quietest kid on the block when cranked, so you might want to turn off the cab sims in your ST and play around with the noise reduction.
I tend to just use the TLST for reverb, delay, chorus and compressor with the Night Train, but I have used it with some of the ST amp & cab models too (classic models eg Plexi, but not really high gain ones) with no excessive noise problem.
It's likely you're picking up unwanted noise perhaps through your ring mains, exterior equipment (eg if you have your computer & screen on), lighting, or through your guitar (particularly if it has single coil p/ups)
Try your rig in a different location & see if there's any difference.
Rich

"I started out with nothing ...and I've still got most of it left!" (Seasick Steve)