Why are Japanese vowels occasionally rhotacised in songs?


This might be a bit weird, but when I listen to Japanese music, sometimes I
notice "r"-like sounds in syllable-final positions, or between vowels where
there should be no [r]. I know that /r/ is not allowed in a syllable-final or
word-final position, so I'm trying to figure out what exactly I'm hearing in
these songs. If there really is an [r] sound in these positions, why is it
legal?

I've tried searching for information on Japanese dialects and allophonic
variation, since I thought that's what it would be related to, but I can't
find anything that seems related. I mostly find things about language
acquisition, like native Japanese speakers learning English, or vice versa,
and generally concerning syllable-initial [l/r]. My only guess is that what I
hear is nasalisation that I'm interpreting as
[rhotacisation](https://en.wikipedia.org/wiki/Rhotacism) due to my own
dialect, but the vowels I hear rhotacised aren't always connected to nasal
consonants or anything, so I'm left wondering why they would be nasalised...

The first example that comes to mind is in the song "Smile Ichiban Ii Onna" by
An Cafe, right around 3:28, where I hear a very distinct [r] at the end of
「たいよう」. Immediately followed by 「さ」:

[https://www.youtube.com/watch?v=TlO2N2t6MA8&feature=youtu.be&t=3m28s](https://www.youtube.com/watch?v=TlO2N2t6MA8&feature=youtu.be&t=3m28s)

The other example is from a band called 摩天楼オペラ. The singer's pronunciation is
often rhotic to my ears. The first line of this song is 「どれだけの善意が どれだけの悪意が
この地上にへばりついてる」, but when he sings 「善意」（ぜんい） it sounds like he's replacing the ん
with a schwar or something similar. And when he sings 「悪意」（あくい） I hear an [r]
inserted between the く and い. As the song goes on, I continue to hear
rhoticisation in various vowels, but not as remarkably...

[https://www.youtube.com/watch?v=WxCie8nujj8&feature=youtu.be&t=40s](https://www.youtube.com/watch?v=WxCie8nujj8&feature=youtu.be&t=40s)

Sorry if this question isn't as detailed/focused as it should be. It's just
something strange I noticed and can't seem to find anything about.

**Possibly relevant information: The other day, I happened upon a [pinyin
pronunciation chart](https://chinese.yabla.com/chinese-pinyin-chart.php), and
noticed another vowel sound that sounds rhotic, but technically isn't
(probably). Obviously, this is a completely different language, but it made me
remember my long-time question here. In the first paragraph below the chart
itself, it talks about the difference between production of the "sh" and "x"
sounds. And while I can't hear the difference between these consonant sounds
themselves, they drastically change the following vowel. Specifically, the "x"
makes the following vowel sound rhotacised to my ears.... but that's as far as
I can get with it. Having my tongue in such a low position (for "x"
production) lowers the following vowel production as well, and also seems to
prevent my lips from rounding or stretching to the same degree as when
producing my normal "sh" sound... But again, I don't notice anything that
would cause a similar lowering effect in all of my examples...

I also realised looking back that I didn't include the very first example of
this I heard: Miyavi's "Jibun Kakumei." I don't hear it anywhere else in the
song except in the word 「[言葉](https://youtu.be/9sLXqM7zGpk?t=3m37s)」, which
sounds like "kerterba" to me. It's softer than the other examples, the [o]
sound has become like the German "ö," or [œ] in IPA...




To me, the singer's tongue is moving backward, and his throat has tension for
"vibrato" in the first one and in the second one. And, I guess this makes you
hear the r sound, something like French R.

French R is difficult for Japanese to hear. I think it is not nasalised
because Japanese can hear syllable-final nasalised sound.

It is said that Arabic only has three vowels [a,i,u], but I found a lot of
other vowels when they used their throat to pronounce. I think they are pretty
similar. A phone and a phoneme are different, and phonemes depend on a
language.

