My MKI is dead silent. Nada - even wide open. I'll second ee3, a trip to ARC seems to be in order.
The only way to know is to use your own ears. To my ears, it is not even close. In your case, maybe there is something going on inside of the pre that is not right. I love the sound of tubes but I have been turned of by the noise, especially from the preamp. There are some good tube preamps. I have never heard the LS25 but Atmasphere, Lamm and First Sound make some great pre's. The Atmasphere uses the 12au7 and unfortunately, it is getting very hard to find quality 12ua7's out there NOS. Both are pretty much handmade and cost well over $5,000.00. Maybe someday I wlll try one of these pres.
Thanks all for your response.
I will call ARC tomorrow. I did a voltage check and everything is good. Although I can read schematics and have some tech skills, I can't figure out where in the circuit this noise might be coming from. If the power filter caps were no good, I would think the noise would be louder and the voltages would be off.
I noticed some strange looking powdery dust covering the main board. I wiped away what I could. No change in noise.