My attempt to translate these descriptions
into not quite linguistic terms.
I believe that for 'Nearly Silent' the authors are
referring to the fact that the Final -R inflection is a non stressed syllable.
To a non linguist this means that it makes less noise than a stressed or medial
syllable. Similar to butter and rubber. Though it is also shorter. Not trilled (
as in classical languages) or held (like in bar room) but short like
in 'short' if you didn't say the -t-. and not like in shore.
And, if i recall correctly, the inflected -R ending
on runestones in represented by the 'pitchforky one' "erhaz" in one text. This
used to be a -Z- sound but over centuries is became zh..then rzh, then R, then
faded entirely.
This is why the rune names are often ending in Z
such as tiwaz, erhaz, thurisaz. This is the Older pronounciation.
There is more of this on
Vikinganswerlady.com.
Ambrosius- Who has yet to find an appropriate Norse
name, though Gummi Bera is sounding appealing.