Share your experience!
When I play a music either via headphone or via Bluethoot speakers I hear sound deformations / noise / Sizzles
Some time I also have the problem when I call.
I've restarted the phone and I still have the problem.
I don't have the phone myself, but my girlfriend is about to buy it.
But your description sounds like the phone has a built-in limiter/compressor.
My HTC had the same issue, and they even boasted that it had "special Beats By Dre sound".
However, that was just a compressor/limiter, that you couldn't turn off.
I guess they put it in there to enhance the perceived loudness when playing music, probably to make up for a lousy amplifier.
The problem with a compressor/limiter is, that the more you turn up the volume, the more the limiter will be working overtime (especially with bass-heavy songs because the bass takes more of the "overall energy" in the mix).
That's why, when you try to turn up the bass the overall mix gets even more overworked and you lose volume.
Often you will hear the whole mix kind of "pumping" up and down at the rythm of the bass drum.
The only "solution" is to turn down the bass, and don't turn the volume all the way up on the phone.
Possibly get some headphones with more surplus.
If you experience a sound distortion while listening to music after the update to Android 6.0, try turning off automatic optimization and see if this helps.
To turn off the Automatic optimization
This issue will be fixed in an upcoming software update.