Hi Dover,
I'd imagine that improved contact integrity resulting from merely changing the fuse is the explanation is some cases, but not in many others.
I can't see how noise pickup could be an explanation, considering the short length that is involved, the much greater length of the associated wiring (both internally and externally to the component), the considerable amounts of noise that are presumably present on the incoming AC, the noise rejection provided by the power supply, and the noise rejection resulting from the
power supply rejection ratio of the circuit stages in the component.
Better materials and construction are often cited as an explanation, but IMO that is a non-explanation, because it doesn't explain (in a quantitative manner, if at all) why the supposedly inferior materials and construction of the standard fuses would degrade the sound.
As you may have seen earlier in this thread, e.g. in the first of my posts dated 5-14-12, and also in the post by Rogermod (the distinguished amplifier designer Roger Modjeski) dated 5-11-12, pretty much all of the other commonly offered explanations do not stand up when analyzed quantitatively, at least for AC line fuse applications.
A point I made earlier in the thread is that all of the comparisons that are reported seem to be between the stock fuse and one or more expensive fuses. But without a good understanding of the reasons for the sonic differences that are claimed, how do we know that a thorough comparison between a variety of ordinary fuses wouldn't result in comparable differences? Perhaps sonic differences would even be found between multiple examples of supposedly identical fuses.
Best regards,
-- Al