The word 'intermittent'. I never heard this word in whole life more than the times i heard ( i should say 'mentioned') this since last two years in my Software Testing Career.
It is common that no is one gonna believe that it is actually a defect until and unless they see it from their eyes.
I was recently involved in a web based application testing which was completely developed under javascript. There was a lot of intermittent issues (actually 90% of defects were intermittent). I had a hard time in explaining the Issues to the Project Manager and Lead Architect since these issues were not reproduciblw everytime. Every time we try to reproduce the defect beforw them we failed.
1. Capture the logs generated during each failures you observed. Logs from one failure will not work, you should capture couple of logs for the same scenario.
2. If it is possible to automate then automate it and run it repeatedly for a fixed and predecided times and observe the pass%.
3. Make sure you capture the screenshots for the failures you observed just to be in a safe side.
4. Communicate all the intermittent issues with the project team. Mostly to your project manager.
5. Keep a track of all the intermittent defects you observed in the defect management tools you use.
Hope it Helps.
Thanks