Tone changes with volume

There's also the little matter that your own hearing perception alters with volume. As the volume goes up, you should hear more highs (and somewhat more lows). At low volumes, your hearing very efficiently concentrates on the all-important midrange. This effect will swamp any impact that a volume control would have.

Sounds like you're not crazy at all. You're normal.

Like Bo says: you're hearing the well known Fletcher-Munson curve effect, which is a bell-curve peaking in the midrange area. Your hearing seems quite normal to me too.

Thanks for the thumbs up.

True. Our ear canals, by their internal shape, are optimized for 2k to 4k frequencies - any thing above or below will very likely cause a change in tonal perception and (definitely) how we perceive relative loudness of certain frequencies. Of course, there is still such a thing as a poorly designed volume pot - but I don't believe the "... shift in tonal balance that results from the changes in impedance caused by the varying positions of the volume control" argument holds any water.