Well, this weekend I started getting a very annoying valve tick after driving up to my parents house for the weekend. I just have a few questions from a relative engine n00b. (2002, LD9)

How exactly does a valve start to tick? When I got to my destination, my car was a bit low on oil, but nothing serious. I went ahead and changed it anyway...I've heard that really low oil levels can affect it, true or not?

Also, I think that our engines have adjustable valves, is this correct? If so, for a ticking valve all I'd need is to get them adjusted so they stop ticking?

It's rather loud, and only gets lounder as the RPMs increase, is this normal? (it gets loud enough so that I can hear it over my radio) Also, I've heard that it's OK to drive on it, and although I have an alternate means of transportation, I want to be sure that I didn't cause any additional harm driving it back to my hometown on Sunday (approx 150 miles).

Thanks!