Installing a low-pass filter is a good idea to reduce radio noise and lower the cpu usage. To install a low-pass filter, use an Atmel ATTiny25, ATTiny45, or ATTiny85 microcontroller and flash it using the plight-firmware package. Follow these easy steps:
sudo apt-get install pilight-firmware
sudo pilight-flash -f /etc/pilight/pilight_firmware_t45_v3.hex
Note: There are different firmwares for the ATTiny25, 45 and 85 (pilight_firmware_t25_v3.hex, pilight_firmware_t45_v3.hex and pilight_firmware_t85_v3.hex). Select the one that matches your hardware, otherwise the filter wont work.
sudo service pilight restart
If you encounter problems while flashing the chip you may try to disable overclocking your RaspberryPI and try again.
The receiver should be less sensitive now. You can see it if you use pilight-receive. There are not that much wrong signals anymore if you press one of the buttons of your transmitter. And the CPU usage is much less compared to the usage without a low-pass filter. The CPU usage should drop to about a tenth compared to the usage without a low-pass filter.