[spiderplant]

Sounds like the sender is picking up interference, either infrared or RF.

IR interference could come from any of these: Plasma or LCD TVs, fluorescent or energy-saving bulbs, fish tanks(!) or direct sunlight.

RF interference can come from any device that uses the same frequency band, such as wireless LANs

try to identify the source, then move things around to make the problem go away.

Also try moving the blaster some distance from the STB or not pointing the remote directly at the sender. Sometimes the blaster sends a signal that is too strong.