separation anxiety?

Question
I adopted a 1 year old terrier mix (definitely has some yorkie in him along with who knows what else) about 10 days ago from the city shelter. I am his third owner.  He is mostly a very sweet dog and seems to respond well to reward based training. He knows how to sit and I have taught him down and to stay for about 15 seconds over the past week. He loves to play fetch. I take him on at least two walks for a minimum of 20 minutes (usually longer) each every day.  The big problem comes when I leave him alone in his crate. He has no problem in his crate when I am in the room and at night but when I leave the room, he begins scratching maniacally at the plastic crate and barking a very high pitched bark.  Sometimes he keeps this behavior up the whole time I am gone (according to my neighbor).  I need to use food to coax him in the crate and I give him a kong with a small amount of peanut butter in the crate. As soon as he eats the peanut butter, he ignores the kong and scratches and barks.  When I let him out of the crate, he is so excited he jumps up (usually about chest level) and nips.  I have tried ignoring him by turning my back and crossing my hands in front of me (as suggested on some web sites I visited)but this is not very effective.  I have also tried putting his leash on before letting him out and making him sit but he thinks I am playing with him. He rolls on the floor, nips at me, and pushes with his front paws.  How would you suggest I work on correcting his behavior both in the crate and when I let him out? Thanks in advance for your advice.

Answer
Shelter dogs often hate being crated.  If the dog isn't destructive and is house trained, you probably don't need the crate.  If you must contain the dog, then you should ignore any noise, whining, barking, etc.  That's hard to do when you have neighbors that aren't so happy about the barking...  Separation anxiety usually implies a dog that is destructive to himself or property when the owner is absent.  What your dog is doing could mean he is simply claustrophobic.  If you think that's the case, you could try containing him in a larger exercise pen instead of a crate.
You are correct to ignore the jumping up and nipping.  But, even better than just ignoring - leave the room entirely.  Once he is quiet and calm, return and reward the good behavior.