If the co. has a very consumer friendly stance, asking and getting a replacement unit this early on ought not to be an issue. Even if its mentioned some more run in time is required first.
A second same unit will do one of 3 things
alieviate the issue entirely, or determine it is a mismatch for your current setup or lastly, some revision is necessary to the current production models.
Each of those items ultimately formulates into a win win situation.
I dont use all the inputs on my tube preamp. It has 4 pairs/sets. It is SE only. Normally Ill use two. A while back after reconfiguring sources on the preamps inputs I mis-selected one of them. I forget exactly which one the selector knob was set to, and while in the other room used the remote to raise the vol. Both sources were on at the time too.
I kept raising the volume and could only faintly hear any source material. Turned out the knob was on a blank spot and the source I heard was on the adjacent or next position over.
So indeed there was some bleed through that could barely be heard yet the volume level to encounter this anomoly had to be at near the max setting.
Once previously on a 100% balanced preamp this exact same thing occurred. In both cases I feel I was very lucky.
During normal operating levels, all other sources were/are inaudible. Again, only when at the near full on vol level or at full on was anything at all audible from an adjacent source selected position
so were talking extremes here.
Not just run of the mill routine operating procedures.
Ive had several preamps and amp combos in here
with some being quite inexpensive and some being very expensive. In none of those mixings have I ever had any bleed thru from one source to another aside from my above accounts.
Lastly
a brand new preamp
SS or tube
should not induce any thunks or plunks audibly to the speakers when sources are changed, especially if prudence with the volume is in force during the source changes
or at least Ive never experienced such things with any pre or even proc Ive yet owned..
Hopefully your brand will see to it you are treated fairly and satisfied very soon.