I just got a Mexican Fender Jazz Bass for my birthday, and I really like it. It feels and sounds good, but when I play certain frets, the bass buzzes a little bit. When I play the open A string, it buzzes slightly, and when I play the 7th fret on the G string (D note), the note doesn't resonate as long as the other frets. Can this be fixed by getting my action lowered? I don't want to return my bass, but I'm just wondering if I can give this to a bass repair person (I know someone specifically) and get all these little kinks worked out by adjust the action. If I do get the action lowered, will the strings feel looser?

Thanks in advance.
It probably is not your action height. Rather, you most likely have a couple of high frets. Have a good technician look at your bass and see if there are any high frets. If there are, a simple fret dressing will solve the buzzing problem.
I had a similar problem when i got my American 5 String Fender Jazz, my D and G strings were buzzing after about the 10th fret and it was driving me crazy. So i took it to a guitar repair guy and it turned out the some frets high up the neck were too high/tall, so he gave them a fret dressing, adjusted my action slightly and redone the intonation and put on new strings and it fixed everything; turned out better than new

so i have a feeling you have a similar problem, this bass repair person you know should be able to fix it rather simply. hope this helps