Resistors

The difference can only be heard if the values are different. What value are you using?

aural acuity is not the issue. The issue is lack of evidence. If you were blindfolded, could you identify which resistor was which 100% of the time? 

What this proves:
1. Auditory memory is a lot longer than some people think; and
2. Parts quality makes a lot more difference than some would have you believe.

you forgot 

3. it could be imaginary. 

Once you get to 5% you might pick up a difference as it can get as high as 10 % between the two which is certainly audible.

which would explain what people are hearing. Just differences in value.