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I had a problem for at least a year or so in my own home, with lights dimming from time to time, for half a second or so.. The one that was most noticeable was in the bathroom, because when it would happen I'd notice the fan slow down for an instant. I checked the switch box in the bathroom, the circuit in the panel, and also looked for any splices in between--in the basement, or the kitchen drop ceiling, anything that could be affecting it. Also checked the main breaker connections, but not the meter connections. I looked at the bugs overhead, they seemed OK sightwise. I have an old FPE panel, and intend on changing out the whiole service in the near future, so even though everything looked OK there, I figured that once it was all new I'd be rid of any problems.
Then a couple months ago, I realized that I hadn't had any of that dimming problem for a while. So I can only conclude that the problem was outside of my house, because nothing I did changed anything. It must have been something with the utility.
Now I don't want to offend anyone if you work for a power company, but I think that in a way, we're at their mercy with this sort of thing. If they say, "It looks OK on our end," how do you know if it is or not? Unless you have a recording meter located on their side of your service, you have no way of knowing. Look at some of those newsltters over at MikeHolt.com, where they have problems with people getting shocked in their back yards from stray voltages, etc. The power company always claims their system is OK. But lots of people believe that there are safety issues connected with the grounding and neutral systems in the power grids. I just have my doubts when it concerns the utilities sometimes...
Hope it works out for you with that testing.