PMP500

Hi,
I am setting up a base station of PMP500; I have 3 APs (model : 3540AP) with about 25SM (model : 3540SM);
Can some suggest a best sceniario of non-overlapping channel i can chose for my AP.
I have selected 3450, 3500.25 and 3550. But it looks like i have self-interference.
I need advise.
Thanks

Bruno