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. Good luck, I'll be interested to hear how your journey progresses.

"...since I can't imagine a tube going bad then miraculously repairing itself."

And, funny thing here... The system is sounding better late last night and again tonight with the Telefunken 12ax7s still in place. Maybe the 15 hours of playing time leading up to a "critical" comparison listen was not enough break in and the additional 10-12 hours is making a difference for the better. We'll keep an open mind and see how things play out.
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I had what might be a similar situation with my Rhea. From time to time I would hear a short duration hissing or rushing sound, but only from the right side. Of course my first reaction was to suspect tubes. During one night of experimentation I changed from XLO to Quatro-fil interconnects between my Rhea and pre just to see how this might change the sound from my turntable. I have not heard the noise since and it has been almost a month. Kind of interesting but probably not what you're experiencing.

I do have some Mullards on my list of tweaks to buy in the coming year.

"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?