potential speed sensor issue
 

89 civic, making a wierd "flickering" noise behind the speedo dial.
needle is steady, but the noise concerns me. if trying to drive 55, the
engine's been stuttering a bit. nothing serious, but if you have the
stereo off, you can hear a brief "ptt" change in the exhaust note every
few seconds. fine at higher speeds & below 40.

so, is this engine behavior a symptom of speed sensor problems? there's
no code, yet.