You should not have any interference problems on channel 4 unless someone else is on that channel with the same privacy code. The privacy code is a sub-audible tone that keeps your speaker shut off until the radio detects a signal with the same tone on it. People will still be able to hear you if they have their privacy code turned off or set to your code. Several years ago, we on Iceshanty set up channel 7 privacy code 0 (off) as a calling channel for members to check when out fishing to see if any other members were around. I made a lot of new friends and fishing buddies that way.
I hope this helps.
Good luckand Happy New Year.
Norm