Hiss at addition in system LAMM L2

I owned a L2 Ref 2 years ago. Had the same issue which drove me nuts. I did everything I could (bought new tubes, rebiased numerous times, changed cables, got balanced cables, moved my rack (thinking it might be and RF issue), took both isolated both pieces from the rack, swapped in another amp. You name it I tried it as I did love what it did in terms of musical presentation. Spoke to Lamm and on their advise shipped both crate "air express" from western Canada to NYC - OUCH at almost $500 return. They could not find anything wrong with it. Since it was there I had them upgrade all the toggle switches to the current version.

Got it back and still the noise but mine was more than a hiss it was more like a sizzle. Had my buddy John Wright of Museatex fame give it the once over - still the same problem.

While it bettered my resident Hovland preamp the Hovland was dead quiet in comparison. In the end I sold it. I could not justify its "issue" for what I had in it.

As Grant advises it may not be for you which was my case...

forgot to add that I threw mine on a BPT balanced conditioner and also ran it on its own dedicated 20A line - still had the problem. Got an email from a gent in Europe after I posted my findings and his L2 Ref had a similar problem. I would imagine what could be this preamp's "best" match is a Lamm amp(s) but that was not in the cards for me...

The pre will hiss no matter what you do. The hiss comes from the mosfets in the circuit and higher gain amps on more sensitive speakers will hiss more than others.
You either live with it or sell it. For me, I chose to go a lower gain amp and it remedied the problem well enough for me.