While driving my headlights will dim and the air conditioner will decrease in power for about 3 to 5 seconds. Then, both will resume normal operation and in a few minutes it will happen again. I have had one person suggest that it is probably the alternator, but I was more concerned that it might be the timing belt. It's an 2007 Sonata with about 65k miles. Suggestions or ideas?

 

It's probably not the timing belt. However, if you haven't changed the timing belt yet, you are 5,000 miles overdue. Should be changed every 60,000 miles or 4 years.