The altered states of clickable buttons and links?

I just completed an Articulate Storyline course and got some interesting feedback from a particular user tester. She requested that clickable buttons/links actually make a "click sound" when pressed.  Upon further inquiry, she explained how she had attended an Articulate training where she learned that some learners, especially the elderly, need to hear (or see) visual evidence that a button does something.  I pushed back a bit and in lieu of a click sound, she requested that a button should highlight, glow, or somehow visually change its state when hovered over with a mouse (assuming they are using a mouse. )

I did a quick tour of several websites: Amazon, Google, and Articulate and found that none incorporate click sounds :) but that some do incorporate changing the state of the buttons/links when hovered over. Others do not. I suspect altered button states may somewhat increase the likelihood of someone identifying a button but it's also moot if we are designing for mobile where users don't use a mouse.  I tend to think that designers must rely on the shapes, text or color to indicate something is clickable. 

Does anyone have any advice, research on this topic they'd like to share?

Thanks!