Has anyone replaced tubes in Aesthetix Rhea ?

"Hi Stew, glad to hear the hissing sound was not present last night. In my experience, tube noise can be intermittent - from one listening session to another. It can be a little unnerving. I've made a practice of taking a deep breath, powering down the system, and coming back a few hours later or the next day. Sometimes the noise completely disappears, sometimes not. I once lived with a really irritating noise in a driver stage tube of my amplifier for a couple of weeks, then it completely disappeared and never came back. What you're hearing is more likely an intermittent problem with a tube than a problem with the unit itself."

I had the same experience with my Callisto.
From the beginning I had a noise ( hiss ), but after some hours of tube burning it went away ( after a few days of use. Possible, that one or the other tube can be very sensitive at the beginning.)

Later I ordered NOS tubes and these worked fine from the very first moment.

Hi Thomas, thanks for sharing your similar experience. It could also be that there was some break in occurring in the tube sockets. I've heard of this happening with a new unit where the connection of the sockets and the tube pins needed some burn in time.
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The intermittent noise I've been hearing I think might best be described as tube "ringing", a high pitched microphonic whistlelike sound. I thought I had the noise licked, but it resurfaced today. It can only be heard at moderate to high volumes. I'm expecting 4 NOS Telefunken 12AX7s this week so I hoping that will wipe out the problem. Any ideas gentlemen?

Sounds like a tube (or tubes), Stew. Only way to know is to swap 'em and see. Let us know how you make out once you change them.
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Rushton, still don't have the new tubes but perhaps you can explain why I would be getting ringing in both channels on some days but not others. For example, last night I had a few friends over to listen to the system. Of course, the ringing was present when I turned the system on and stayed all night without abating. Tonight I'm alone and I turn on the system and other than the usual tube rush one might expect to hear, all is quiet. The night before last quiet too. Like you say, the only way we'll know if its the tubes is to swap 'em out. At the moment, I only plan to swap out the 12AX7s in the first gain stage. Any reason to think these might not be the culprits? This is just too strange.