See: http://www.google.co.th/search?hl=en&q="squeaking noise of s...

an alternative

I think the synonym 「軋轢」, which means "friction", "strife", or "discord" can be used in this instance.

Instead of throwing random dictionary definitions for the words together, we need to think about what the person is actually trying to say.

They seem to be talking about how the dissonance between two notes becomes more pronounced and extreme as you move them lower and lower into bass registers. If you play a perfect fifth on the bottom end of a 5-string bass guitar, it almost sounds more dissonant than a minor second on the top strings of a guitar. If you've ever tuned a guitar by comparing strings, you can clearly hear how the frequency of vibrations change speed and get more or less intense as the interval between the two notes played against each other becomes more or less dissonant.

Without any context, I'm guessing they're contrasting the contrabass to similar but separate (in the writer's assertion) phenomena in the mid-range, where they're saying that it sounds like there's a glissando (slide) going on continuously, and in parallel, in the upper registers, where they're also using some sort of strange metaphor, describing the sound itself with the word 軋み, while 天空 is also just added perhaps just to describe the direction that the writer feels like the sound is coming from, since the pitch is "higher", to invoke a more vivid image in the reader's mind.

So since this is a scientific description and not song lyrics, I wouldn't get too pretentious or overly poetic and dramatic with words like "ethereal" or "heavenly", because they're not adding some kind of extreme positive emotional value judgement to the phenomena, but rather just describing observable scientific phenomena in physical terms via a metaphor of where the sound is coming from. So I would just say "in the sky," "from the sky," or "against the sky."

Then which translation you choose for "軋み" I suppose is a matter of how you interpret the original intent. It could be "creaking/screeching up in the sky," "grating/scraping against the sky," etc. If they're talking about violins and other bowed instruments, I would imagine myself that they're imagining dissonance between violins that sounds like something scraping against the sky, like nails on a chalkboard. Except that there's nothing actually to scrape against in the sky because it's all air. But I guess sound is just moving air, technically. Once again, weird metaphor.