Has anyone replaced tubes in Aesthetix Rhea ?

I have developed a high pitched hiss from the stock Sovteks which came with my unit. I believe its at least two or more of the 12ax7s which are in the first input gain stage as I hear it more or less equally out of both channels. I was wondering if any Rhea owners have rolled the tubes in their units and, if so, what prompted the swap and what success you have met with.