I am a newby to this also. But, I bought the tools and trued my wheels a few months ago, because it is an hour drive to my LBS, and unless I am headed there for a purpose and can safely leave my bike outside, I don't go. So, I learned to true my wheels, and I have yet to do it again. I check them by spinning the rims, before I leave on any ride, but they haven't changed in the last 400 miles. I run my pressure at 120 and I am on 700 x 23 tires.
Are you checking your air pressure regularly, and do you keep your cadence up also? I seemed to have more problems when I was mashing instead of keeping my cadence around 90 - 100. I have hit some major rocks/cracks/bumps/etc... while riding on the highway shoulders lately without any problmes.
After talking to others, I will probably need to get the proper tools to adjust the tension of the spokes equally. I have always used the "ping" tests on my motorcycle rims, and was using a similar approach to my bicycle spokes. The difference was a metal wrench on my motorcycle rims and I use my finger with the bicycle.
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2007 Jamis Ventura Comp
2006 Jamis Explorer 2.0
2000 Specialized Hardrock (bought used)
Swim, Bike, Run and sounds like fun