high strung sheltie

Question
Hello, I'm looking for a suggestion on how to handle a pretty high strung sheltie.  He's 8 mos old and we've had him since he was 3 mos. He's been neutered.  We recently added another puppy, a 10 mos old boy that will be neutered tomorrow.  The younger guy seems really stressed out and neurotic.  Seems almost everything sets him off but particularly when we open a door, move a gate, or there is something that makes a noise.  He barks and scratches to get at the door (not out, but at the door)and gets very 'angry' at us when we pass through the door or step past the gate.  He then frequently starts running around sniffing the ground in a regular pattern for about 30 secs, then will calm down a little.  He also tries to attack cars when walking or when he's in our vehicle.  Both dogs get 1 mile morning walk, a 2 mile evening walk, and generally lots of chasing each other around the house.  They seem to get along well, no aggression between them.  They both also do well with people and other dogs. We are looking for suggestions on how to address his behavior around the doors, gates, etc. and keep him more even keeled.  I will mention that they are by themselves 6-7hrs a day in their own x-pens.  Any suggestion is appreciated.  Thanks!

Answer
These guys need training - that will give you more control, and them more mental exercise, which in itself is tiring, too.  My advice is to take them to a positive training class - herders do not do well with punitive training, and they're so smart they generally don't need it.
But, because they are smart, they need a job to do.  If you don't have sheep, the job could be obedience, agility, rally obedience, canine freestyle, etc.  Shelties are alert barkers, and they are quite famous for being noisy, but you can teach them not to be quite as loud by allowing them a few barks to alert, then "quiet".  I prefer clicker training for that purpose, but if you live in an apartment or home where your dogs might be in danger of eviction or complaints from neighbors, you can try a citronella collar.
www.clickerlessons.com has some free lessons on their site to give you a start, but I would take the dogs to a class, too, so that they are well socialized.  Best plan is to take the younger dog first, then the older one later - not both to the same class.
You can find a trainer at one of these sites:
www.ipdta.org
www.peaceablepaws.com
www.trulydogfriendly.com
www.apdt.com (ask if corrections are used, if so, say no)