Tilly, do yours have a high pitched squeal when you get really, really close to something, I find that most annoying, more annoying than the husband in fact.
One does not normally try to reverse into something so is the volume control really necessary ? As long as it is loud enough to hear.
Foolishly I had front sensors added to my car when I first got it. Never used them. Was told they had to be off normally or they'd start sounding when in jams and waiting at lights etc. One would have hoped they'd sense the difference, but not apparently. and I can never be fussed to turn them on and use them when parking anyway.
factory fit or aftermarket ?
Aftermarket often have a switch on the control box with 3-4 levels,unfortunately its often hidden behind one of the rear inner 1/4 trims, not quite so easy to get to.