Choppy calls one way

Hello all

we are having issues with our calls becoming choppy through our asterisk box.

the agent can not hear any problems but the caller can, the call sounds broken up

we are currently using codec G711U

local internal calls sound fine, i thought it may of been caused by sip trunks but even calls coming into our FXO box is still effected

any ideas anyone?

does this sound like a codec issue?