Radios or music players? They behave differently. In any case, you may need to turn them on if they somehow got turned off, or turn up the volume if they somehow got turned down, or choose a new song if they're music players. You might try picking the items up and then displaying them again, and see if that fixes it, if you haven't done that already.
I haven't had this issue myself, but I only ever had one music player set up outside, maybe having more than one somehow caused a problem, so maybe picking them up and putting them back might correct it.
Which items are you having this issue with specifically? Do other radios/music players function as expected?