Found this service bulletin dated 21 JAN 2016
NUMBER:
737-16-1
767-90
777-41
DATE: January 21, 2016
SUBJECT: False Weather Returns with Honeywell RDR-4000
ATA NO: 0200-00
APPLIES TO: Airplanes with Honeywell RDR-4000 Weather Radar Processor P/N 930-1000-001 installed.
REASON: To provide information on the false weather returns.
BACKGROUND INFORMATION
Over the course of several flight tests conducted at Boeing, several instances of false weather indications have been noted with the RDR-4000 Weather Radar Processor P/N 930-1000-001.
Investigation by Honeywell and Boeing concluded that the cause is externally generated radio frequency (RF) signals, or RF interference. Depending on the source of the RF interference, the false weather may show rapidly and dissipate over time. The false weather indications do not interfere with the ability to detect and display actual weather.
Below are examples of the false weather indications.
(Pics of false WX radar returns)
When the RF Interference is no longer present and the memory is refreshed, the false weather indications will no longer be displayed. It may take up to 30 seconds for the memory to refresh.
Testing and observation on several aircraft has confirmed the issue is not related to faulty equipment, equipment configuration, or installation.
BOEING RECOMMENDATIONS
Honeywell WXR Radar Processor P/N 930-1000-003 has incorporated improvements in the radars ability to reduce the susceptibility of the system to externally generated RF signals. The 930-1000-003 part number is planned to be certified in March 2016. If operators are experiencing this issue, contact Honeywell for a service bulletin to update existing 930-1000-001 part numbers to the 930-1000-003. Reference Honeywell Service Bulletin 930-1000-34-14, Publication Number D201412000015.
Hope the above post helps.