Doesn't sound like this is necessarily an emitter-related issue, but it could play a role.
I had some interesting results when running at max with different AA cells last night (D10 GDP). I found that with a NiMH (1.2V, eneloop) it got a bit warmer than with a 14500, but not by much (maybe 5 degrees). Then I tried a standard alkaline (1.5V, duracell) and it got warmer still, but not hot (maybe another 5 degrees). Then I tried a lithium primary (1.7V initial, energizer) and it got significantly warmer, bordering on what I would consider hot (easily 10 degrees warmer than the alkaline).
In all cases I ran for 20 minutes, tailstanding in a cool room. I am happy to report that the light appeared to remain in regulation for the enitre time in all cases, so once again it sounds like your light is most certainly defective. I also noticed that I have a noisy inductor when using these lower voltage cells. Oddly enough, I found that tapping the light could change both the frequency and amplitude of this sound (there appeared to be no relationship between these variables, which would rule out my own ear's sensitivity being to blame), in some cases I could get it to a point where it was barely audible, but in other cases it was kind of irritating.
Anyway, good luck with the repair - I'm sure you'll be well taken care of. And...
:welcome: