There is no ramp control on Tx. What you can possibly try is setting the attenuation high so that the output signal is low 9as an experiment) and see what kind of influence that has.
Have you tried correlating to ADI evaluation platform?
Another suggestion is to make sure the PLLs are locked by reading the Lock bits.
What do the supply rails look like as you switch Tx/Rx? Do you see a transient there? 1.3V supply has +/-2.5% tolerance.