Interference from 5 KHz EM transmission from POLAR Heart Rate Monitor.

We have designed and installed wireless BIKE computers using XBEE. We have two issues,

  1. When multiple bike’s are installed, we have collision and loosing lots of data
  2. When we are trying to use POLAR Heart Rate monitor that uses 5 KHz Electromagnetic wave for data transmission, it screws up nearest XBEEs and we receive some garbage data.

Any body, any hint how to prevent these issues?