Vowelized Consonants?

Hi, people...

I was trying to figure out what exactly the difference between {t,}
(cedilla'd) /s/ and {z} in my still-nowhere's-near-finished new conlang,
Judajait is, when i noticed something weird.
The difference i found is that "soft {t}" is pronounced with a lax jaw,
while the more hissing {z} is pronounced with the lips moving into a sort
of grimace or smile configuration.

So i tried that with another consonant, namely /k/.
It sounds like each jaw-form has it's own default vowel:

normal /k/ sounds like /k@/
grinning /k/ sounds like /kI/
lips-rounded /k/ sounds like /ku/
jaw-dropped /k/ sounds like /ka/

Is this a known phonological fact, or am i just imagining it?

And does anyone know how in IPA to mark these kinds of consonants,
specifically the grin-hissing /s/ ?

thanks,

-Stephen (Steg)
 "hhalomot zeh b'emet"

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