For a long time I suffered some kind of interference, too. After a great deal of research I believe that the source of the interference is my smart power meter, which transmits in the same band as the PDA.
The default channel used by the PDA is 5, which directly overlaps one of the channels of the smart meter, which uses frequency hopping. After perusing FCC licensing documents for the smart meter and the PDA, I determined that channel 4 is the best solution for me. So far it has made a big difference.
If you are currently using channel 5, try channel 4 instead. If that doesn't work, try a few more.
The PDA works in the 915 - 930 MHz band. Knowing this may help you find other sources of interference.
Good luck.