Hi. My radio constantly flips between stereo and mono with the accompanying change in volume and quality even though I drive in the metro area 99% of the time.

I realise that my car (1993 525i Touring) has the diversity antenna in the rear side window.

Whats the most popular or common solution to this problem?

Is it a matter of an inline signal amp, or changing to a different antenna perhaps?
What have most people found works best please?