|MadSci Network: Earth Sciences|
The quick answer to your question is that, although sometimes for certain it can be windier at night than it is during the day, the reson you hear your windchimes more is because it is likely much quieter. Since, in most places in the world it is generally much windier during the day than it is at night (In my reasearch in North America, I typically find it about 30% windier during the day than at night).
You are correct in assuming that changes in pressure cause wind. One of the major driving forces behind changes in pressure is temperature gradients (ie air moving from an area of low temperature to an area of high temperature), and these tend to be highest during the daytime, as the sun heats different surfaces over the course of the day.
This is the reason why winds are typically greater during the daytime. In the wind energy field, for example, people who own wind turbines expect to get most of their power during the day, when winds are highest ( http://www.windpower.org/en/tour/wres/variab.htm).
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