I use a Bluetooth speaker with a 2016 MacBook Pro. Sometimes the sound would become unlistenably choppy unless I moved the speaker as close as 1 m to the computer. Normally I use it from a distance of 4-5 metres.
Finally, I discovered what triggers the problem: an in-progress Time Machine backup to a directly connected external hard drive. The sound becomes choppy only when the external disk is being used. It is not correlated with CPU usage, which is never high.
Is this behaviour expected? Is there anything I can do to maintain the quality of the Bluetooth connection even when running a backup? Is the problem caused by radio interference from the hard drive, or some sort of "slowdown" of the computer (e.g. too many hardware interrupts)?
I should note that the speaker has a perfect Bluetooth connection to other devices (such as mobile phone), even when those devices are placed next to the computer during a running backup. This led me to believe that the problem is not simply due to radio interference, and gave me hope that there may be a fix.