I hate to sound pessimistic, but welcome to the Mesa Boogie club. You can read extensively about my issues with hum and my Roadster. I don't know about the plain Dual Rectifiers, but according to Mesa's tech, and much to the chagrin of my local tech, the noise is normal. Yes, that is right, they said it was normal. I made myself crazy buying new tubes for it, taking it to two different techs, etc. What's funny is that when I went to my local Mesa dealer who had a Roadster head and 212 combo, neither did what my amp does. They sound exactly how I remember my amp once sounding.
I don't know what is up with Mesa's amps, or my amp right now. I've searched the archives of this forum and found people with Roadsters who have had or are having similar issues. Coincidentally, Mesa boasts that they have a quiet effects loop on their Roadster, and better yet they are a series effects loop, yet somehow their tech has the audacity to make me feel like I'm crazy for:
a) using it
b) using it past 25%
According to him, you should never go past that point. Humorously, at 50% or 12 o' clock, the amp specifically states this to be the "normal" range. Normal? You mean noisy range, don't you?
I feel like I have helped further this notion that Mesa's are the end all be all of quality amplifiers. When I first got my amp I rushed to Harmony Central to make a review in order to help other buyers find the "tone" that I had found. Yet, throughout those reviews, I'd always come across these little solo reviews, stating that the effects loop is noisy, the amp is noisy, there is a static hum that wont go away, etc.
Love your amp for what it is, and don't let it drive you crazy. I, unfortunately, have lost my mind.