Caller report echo on multiple ROMs

I posted this in the Sprint note 3 section but realized that was silly as I have confirmed this is not a Sprint specific issue.

My callers report an echo. I sound fine to them and everything sounds fine to me; They hear their voice echoing back.

This does not happen running stock TW. either 4.4 or 5.0
However EVERY ROM I try, I get it. What gives?

ROMs tested and confirmed to echo:

(All on 5.1)
Cm 12.1
AICP
Dirty U.
Temasek

I'm UTD mainly on them all
(since mid-late July)
Doesn't matter which nightlies I try ect.

Most of the time you read about these issue they get chalked up to the phone case. This is clearly not the issue here.

I'm a newb to romming (is that verb?) Could it be by chance my gapps? As I do flash the same gapps on all...

This sucks because the stock TW (rooted ect) actually has more problems than anyone of these ROMs, but not the voice problem which is to great to bare.

On the AICP G+ group other hlte users reported it (non sprint)
Some say it comes and goes.
I don't voice much so its a little non issue for me but grand in it's effects.
FWIW This happens on landlines as well as mobile networks.
I read that this was an old CM issue fixed months ago....But I didn't flash CM12.1 until mid July nightly.

-Thanks