My daughter exhibited the same behaviors at this age...and I hate to tell you that she wound up with a diagnosis of Sensory Processing Disorder and PDD.
That does not mean that every child who exhibits these behaviours has a developomental disorder, by any means. Some of the symptons of Sensory Processing Disorder and PDD/Autism Spectrum look like behaviour issues. The key is whether or not typical discepline works to correct the behavior.
If not you might need to make yourself aware of the signs and symptoms of developmental disorders so that you can get on top of any such situation, if it does exist.
Some really big warning signs for PDD/Autism include poor eye contact, not responding well when spoken to or his name is called, and repetative behaviors (stimming).
Here are two website for symtom lists,
http://www.sensory-processing-disorder.com/sensory-proces...
and http://www.nimh.nih.gov/health/publications/autism/comple...
If you think there is a problem early intervention is critical. Don't let anyone tell you, "just wait and see." Diagnosis can be made by Occupational Therapists and Psychologists. And treatments include therapy and biomedical intervention (called the DAN! protocal) for both conditions. My daughter has received these treatments and at six has recovered.
Good luck and I hope my advice is not needed but the best thing you can do is to at least make yourself aware of the warning signs.
P.