Some people just suck. Others may be frustrated with the work added by having a newbie around, or just not be good teachers - not everyone is.
It may be their problem and not yours, but to make your life more pleasant, try the old adage "you catch more flies with honey than vinegar". Nothing annoys bullies more than being confronted by a pleasant, friendly person who doesn't react to their rubbish.
If they are criticizing you, try saying something to the effect of "I really appreciate your input into my development. I'd love to try and meet your expectations - can you give me some specific examples where I could improve my practice?". They usually can't. If they can, great - maybe you can learn and improve, and enjoy a nicer relationship too.
A lot of these old cronies just want you to acknowledge their experience and wisdom. If you buy into it for your own good, and appear to be LISTENING, and taking their suggestions on board, they often back off and end up being helpful. I had THE most crabby witch as an associate charge nurse in one of my first ICU jobs - she was always bitc*ing at me, taking over, saying "oh, let me do it!", etc etc.. after a while I decided to quit being defensive and listen, and several years later I count her as one of the best nurses I've ever worked with. She taught me a lot.
So - in summary, maybe they are just misery guts, but try being a willing learner and take advantage of their knowledge, and see what happens. Good luck!