Am I being petty at work?

[Maybe2]

Genuinely open to brutal feedback here.

i started a new job in summer as a senior manager, and think my arrival has put out the existing members of my manager’s team (my level colleagues). There’s a lot of lip service from them in his presence, but hostile behaviour when he’s not around (and tbh, sometimes when he is around). My manager is okay with me and has given me good feedback/a bonus and lots of autonomy.

for example my manager wants my team to bond with the other teams. So I sent my level colleagues resources that have helped, invited them to my team meetings with guest speakers & put them in touch with my network, which has even led to them taking credit for some of my ideas & getting a bonus. Equally, they never do the same for me or my team, completely freeze us out of useful things. Get the impression I’m stepping on toes etc.

when I asked them for help (once), in a group setting they rolled their eyes and said my predecessor never had this issue. I know my predecessor did as they informed me in my handover so I found that rude. My manager didn’t say anything. Therefore I limit my interactions with them, but now it’s turned into a concerned “we never hear from you”. Almost as if I’m not being a team player?

also there’s occasions where they’ve randomly tried to do my work for me or pulled the rug from under me and I feel patronised. They also are outwardly bitchy about other people in our team meetings and I get the feeling they do the same about me when I’m not around

Discuss it with your manager in a very matter of fact way. Don’t bottle it up.

He’s kind of part of the problem cause he doesn’t address any of what he witnesses though eg bitching about colleagues in meetings

It sounds like your manager needs managing upwards!
good luck op

i keep hearing about that but not sure how to approach it

I hate people like that YANBU

Why didn't you speak up about your predecessor? It would have been easy to say oh but they did…

Honestly, it seems like two things:

1 - I can see how your attempts to foster inter-team communication have resulted in them thinking exactly the same things as you - somebody trying to do their work randomly and getting in the way, patronising as though they don't know how to do their jobs etc.

2 - This is the kind of baked-in culture that sinks companies, and once it's there then little can be done to fix it without mass personnel changes. Keep a couple of recruiters in your back pocket.

It sounds like a dreadful environment. If I had to deal with these 'level colleagues' literally daily, sit near them etc, I think I would be needing to leave the workplace or at least remove myself fully from them.
Your manager is not managing and you seem really unhappy.
If you can't ignore them nearly all the time I would go. Don't try and more inter-team interactions or whatever as those initiatives didn't work, and surely they don't fell upon you as part of your direct role?
Is there a senior person you are friendly with in a slightly different area who knows these people, maybe ask their advice or if they have noticed anything from their side. Members of these other people's teams can't be happy either surely?