The HTC one hissing noise
I just activated an HTC one on Sprint 5 days ago and the call quality is very bad. When "on ear" and speaking to a friend on his land line, he notices a drastic difference in quality relative to my old Motorola XPRT phone. He describes the very same thing we are describing here....buzzing or static underneath the other person's words until they stop talking. Also, he speaks softly sometimes, or puts me on speakerphone and I can barely understand him because his voice cuts in and out.
Similarly, while I was on the phone with HTC about this yesterday, their hold music was doing the same thing, cutting in and out. It seems that anything with a low level will do that.
In the music recording world, we use a "noise gate" to reduce noise like hum on an electric guitar, and that's what it sounds like to me on the HTC one. When the other person stops speaking, the "gate" closes and we hear silence, until it detects signal (voice) and the "gate" opens again.
This is even more obvious when using the supplied earbuds. Right when the call is connected I can hear an abnormal level of noise, over and above what we're talking about, which is something I am NOT used to with my mobile phone. I have been on Sprint since 1997 (yikes) and the call quality has always been superior to any other carrier I've experienced...until this phone. Again, my old Motorola was like talking on a landline most of the time.
So I am really talking about two specific noise issues. Mainly, a buzzing or static while the other party is speaking, and to a lesser extent, a sort of general noise under everything.
I've also updated to the latest Sprint HTC one software (released 7/17/13), which said it included HD voice updates, but to no avail.
Best of luck everyone. Any new information please follow up.