laser cavity :

when one decreases the laser motor position, the laser repetition rate increases (laser cavity length decreases).
=> +/- laser motor step  =>  +/- laser cavity roundtrip length => -/+ laser repetition rate => -/+ laser harmonic @500MHz 
=> +/- 100nm => +/- 200nm => -/+ 0.7Hz @33.33MHz => -/+ 10Hz @500MHz

here is the natural variation of the laser cavity frequency beating with RF @500MHz over 1h (~1.6s / iteration)
one can see some oscillations equivalent to ~1µm of roundtrip length with ~10 minutes period and maybe a slower drift or oscillation with ~2µm of roundtrip range over the hour.
I mention that I moved the laser "PZT" motor before taking the data : could it be the reason of the 10-20min oscillations ?

during the same time, here is a probe temperature curve (the probe in stuck on the end flange, close to X-hutch, of the FP-cavity, inside the housing... not close to the laser position).
the temperature variation range is ~2.5/100 °C which induces on inox (relative length thermal effect : 17e-6 /K) a length variation of 4µm of roundtrip (10m) which could be compatible to the laser cavity length variation measured.