healthy piggy?

Question
i've only had two guinea pigs in my life timetime. my first one i only had for two weeks because he died of a virus that affect his central nervous system (lymphacitic coreomeningitis virus). It was the saddest thing I've ever seens, but because he was my first and had him for such a short time, I am not sure the true behavior of a guinea pig, so with my new guinea pig I am not sure.
  I think my guinea pig is very healthy, but he is doing things that my other piggy didn't do (I think it is because he IS healthy and my other one isn't, but I want to make sure and see if I need to take him to the vet)
  The first thing that my piggy is doing that I've never seen before is he is jumping in the air like a wild thing. He jumps in the air and like shakes his head then runs around and does it again. I have heard of popcorning, is it that? Do they shake their heads and run when they do it? The only place he does it is in his cage, he never does it in his play pen or anywhere else. I just want to make sure that nothing is bothering him like mites or ticks to make him jump and shake his head? He looks so funny and cute at the same time.
Next my guinea pig kind of shakes his head and body like a dog sometimes. He shakes it maybe five times a day. I heard from some sources they're not supposed to do this, but from other sources they do do this. He scratches himself a few times a day, but nothing accessively I do not think.
Thirdly when I first got him he was sneezing a good deal. I was wondering if that was just him getting used to the new environment because now I only hear him sneeze five times a day tops. Is that normal?
Lastly, my piggy is barely making any noises. He is 3 months old and the only time I have ever heard a noise is once when he was in his play pen walking (kind of a grunting noise like a real pig) and then once he was on my shoulder smelling my hair and i was petting him and it kind of sounded like a purr i'm not sure what noise it was. Other than that he is 100% quiet (I want to hear noises!!) and when he is on me he almost is completely still the whole time (I've only had him for less than a week so I think he is still frightened) Will he start to move around and make noises? Thanks!

Andrea
age 20

Answer
It sounds as if your guinea pig is simply popcorning.  Shaking like a dog does is not uncommon.  Especially after they have been handled or have just groomed themselves.  Not a lot of sneezing is a good thing.  If he is sneezeing to much it might be due to dust in his bedding.  If your guinea is still new then he just needs time to adjust and settle in and he will become a normally little piggy.  However, if you still have concerns, please take him to a vet immediately.