I am familiar with this problem and although there is nothing wrong, it can be quite annoying. I have installed 40 or 50 recessed cans in my home at different times as areas were renovated. I have used a variety of types and manufacturers of cans and I have discovered that the cheaper the fixture, the more likely it is to pop. The first 18 I installed were very expensive and I have never heard them pop. The last 16 I installed in another renovated area were considerably less expensive and every one pops when the lights first warm up and when they cool after they are turned off. This seems to be the major difference between a $35 fixture and a $120 fixture because they are all Alzak reflectors and have similar quality light distribution and cut-off angle.