Noisy Calculator, the SR-56

One very interesting feature of the Texas Instruments SR-56 calculator was that it was noisy. I know that sounds strange, but if you held it up to your ear you could hear some quiet humming noises. If you used a trig or a log function it would change the sound as it worked out the answer. I can't think of any other digital devices I've ever owned (actually this particular calculator belonged to my brother Billy) that make noises you can hear. Sure, you can hear your cell phone blasting out data packets over your stereo or PC speaker system, but that's radio interference. This was actual audible noise. I wonder if they made any other noisy calculators back then.