When the DF window is visible, the laptop speakers make a constant, soft, almost inaudible noise. They certainly shouldn't be doing that. I have headphones connected, and the laptop speakers should pretty much stay quiet no matter what. I find this absolutely baffling. It only happens when the DF window is visible on the screen, and updating; that is, not when saving or loading a game. It's quiet enough that I can ignore it, but still kind of creepy. DF sound is turned off from the init settings.
My guess: The noise is caused by the heavy work your GPU is doing, assuming you get the sound only in 31.04
You don't have any idea of just how much I envy you that your computer is good enough for you to be able to consider 40 fps abysmal. Sure, on my desktop, I usually get around 250 fps too and that's good, but on my laptop, 25 is the norm (even in the previous version). And it's still fairly playable, I'd say. I also haven't experienced anything that could be described as "interface jerkyness", maybe it's an unrelated issue.
7 idle dwarves at embark @40FPS means 30FPS once they get to work, 20 FPS with 20 dwarves and open caverns and at 60 dwarves it becomes unplayable - and in comparison to 31.03 on my (fairly old) machine that is abysmal. For a "speedup release".
Seriously, I'm playing with a fairly
cheap laptop bought over an year ago (HP 6735s) and I'm able to kick 58fps with 57 dwarves. SHADER seems to work the best, but ACCUM_BUFFER and FRAME_BUFFER still give me a nice ~55fps. With 31.03 this would be unplayable for me ..
I don't know what is your definition of "fairly old", but even my old desk computer makes better FPS than this laptop. And that fella has an 8-year old GPU (radeon 9600), though the processor is a bit newer dual core.
Maybe time to move on from the 486dx4?