The E-Jets will have new Honeywell integrated Antenna drive, R/T and processor units. It's all a one piece deal called an RTA. No waveguides snaked through bulkheads anymore.
Once upon a time I used to perform maintenance activities on a number of different airline and business airplane types equipped with the older style Bendix or Sperry/RCA systems. This occasioned the removal and installation of many RTs and antenna drives. Getting the waveguide perfectly aligned and secured was essential to preventing moisture ingress and other installation induced problems. Improperly installed waveguide filters, mating flange seals and saturated dessicant were often related to wx radar discrepancies. Poor radome condition is another leading factor in various radar performance issues.
Later, when I began flying with these systems I noted a correlation between moist conditions and an increase in display "fuzz" or "noise". When I began flying somewhat newer airplanes equipped integrated EFIS panels and modern radar, I noticed the same thing, but to a somewhat lesser degree. Better noise filtering, sensitivity/gain control or other display processing functions on the newer units perhaps? Better protection against moisture ingress? All of the above? Probably!
In my experience, the appearance of the anomalous "noisy" returns seems to occur most noticeably when there is little or no precipitation returns being displayed and when descending into moister air. When areas of moderate or greater returns are displayed, the fuzz is less apparent and does not seem to interfere with the display of legitimate returns. So in my personal experience using the radar, it's never really been worthy of a written discrepancy. I've asked avionics techs about it informally and they haven't come up with anything more definitive than what I have. One old Westwind I used to fly had some serious radar issues, but they were the least of the that airplanes problems!
Other than that, even older wx radar usually seems to work well enough in spite of some distracting anomalies. The new stuff is fantastic and getting better all the time.