Your problem is fairly simple in nature:
You are utilizing an analog DC controller while locomotive is equipped with a sound decoder for digital command control and is optimized for use with a DCC system/controller.
You have three solutions as I see it.
1. Upgrade to a DCC system whether that be a Bachmann product such as the EZ-Command system, the Dynamis Ultima (more readily available in England) or any other DCC system of your preference. Note that other companies have their own proprietary systems that only have limited DCC capabilities such as MTH's DCS.
2. Remove the sound decoder and speaker and install jumpers.
3. Be content with the status quo
You are utilizing an analog DC controller while locomotive is equipped with a sound decoder for digital command control and is optimized for use with a DCC system/controller.
You have three solutions as I see it.
1. Upgrade to a DCC system whether that be a Bachmann product such as the EZ-Command system, the Dynamis Ultima (more readily available in England) or any other DCC system of your preference. Note that other companies have their own proprietary systems that only have limited DCC capabilities such as MTH's DCS.
2. Remove the sound decoder and speaker and install jumpers.
3. Be content with the status quo