Take the shocks apart again, I think I know what your problem is. With the foam bobbin in the shock make sure it is soaked with oil. The best way to do this is to compress the foam and soak the bobbin. Then when you let go of the bobbin it sucks the oil into the foam. Also make sure you coat the o rings with oil. If this does not work you may have a broken o ring, so check these as well.
You can even fill you shock with oil get the air out of them the best you can and leave the shock un capped over night. The think that Fat Doggy was talking about it a vacuum pump. A little expensive but these things are great.
Also remember when putting the cap on half fill the shock cap. You should get you rebound right. Shock shaft should come out slowly, just make them the same. Doing all this you should not have a problem and have anti noise shocks.

Coxy