Astra radio keep switching stations

[-Lummox-]

My other half has just bought a 2006 Astra and it has an annoying habit.

It has the standard stereo and won't seem to stay on station. I'm guessing it has an "alternate frequency" setting turned on, but the stations it flicks between are completely unrelated so it's very annoying, and I can't find where in the menu to turn off the setting.

I'm pretty sure this isn't being caused by the TP function (and changing that has no effect anyway). Can anyone help?

Cheers