My 1 yr. old St. Bernard rescue whines all the time is it to get attention or anxiety?

We rescued him about 3 months ago he was abandoned in a foreclosed home. He was in a foster home for a while with 3 other dogs and several cats I have done obedience training with him and I am home a lot with him or he goes with me when he can. He whines when he is not getting attention, when we are getting ready for work, going to bed, around other dogs or has to go outside. We have days where he will not do it at all and other days when he won't stop. I have had a professional asses him and she thought it was a nervous tick, like when humans bounce their legs for fidget. She gave me a few tricks to help and it has not worked. He gets a lot of attention and is part of the family. I would like to know how to stop this behavior with tips and tricks and maybe why he is doing it. Anxiety, stress, boredom or just being a pain. He is healthy so I am not worried about him doing it because he doesn't feel good. Thank you :)