Before updating ubuntu 8 04
It's from either the 1/f noise of the electronics or if it's a Zero-IF tuner (E4000) the LO beating with itself in the mixer.My favorite way to explore the spectrum is using rtl_power to do very wideband multi-day surveys.osmocom_fft comes with GNU Radio module gr-osmosdr and is the natural and best way to use gr-fosphor; a GPU accelerated display.
You can cut the leads to the LED to drop usage ~10%.
The rtlsdr RTL2832U chips use a phased locked loop based synthesizer to produce the local oscillator required by the quadrature mixer.
The quadrature mixer produces a complex-baseband output where the signal spans from -bandwidth/2 to bandwidth/2 and bandwidth is the analog bandwidth of the mixer output stages.
For command line and low power devices try keenerd's rtl_fm.
These sites maintain the best list of rtlsdr device supporting applications: https://sdr.osmocom.org/trac/wiki/rtl-sdr#Known Apps, https://sdr.osmocom.org/trac/wiki/Gr Osmo SDR#Known Apps, and lately Assuming you're on linux, but applicable in general, do not use the OS DVB drivers.