On my droid I get a pretty much non-stop sound during calls that sounds like running or rushing water. it's subtle, but definitely annoying. I used to be quite a whiz a few years back on verizon phones and their network but sadly time passes..
It pretty much exists during the entire call, I can't say for 100% if it is while we are talking (only dead air issue) or what. I did do the evrc tweak but kind of lost as to what else to try.