Hi,
I don’t believe that it is possible to disable this feature as it is built-in to iOS.
I believe what is happening is the fact that the volume on your headphones and the volume that your phone puts through to the headphones is different.
Try re-pairing the headphones with your device and that may work.
If that has no effect, un-pair and “forget” your headphones as a device, restart your iPhone, re-pair to your headphones and that may work.
If none of those methods work then visiting the support pages of the companies that you got your headphones/speakers from may help.
Cheers and Stay Safe