Please be honest in how you communicate. Then you won't have to worry about it and you'll have the benefit of being honest. Assuming the programs are not otherwise linked, they are unlikely to speak to each other pre-ranking. The PDs have other ways to spend their time. You will not be ranked based on these LOI you send anyway.If so, about what?
At this current stage, if contacting PD's to say you're very interested and they're a top choice- if you send multiple ones, any chance of them talking to each other? Does it matter if they do?