This sounds very similar to a common problem with the Blaupunkt radios fitted to 156s. The solution on the 156 is to keep a CD inserted in the drive at all times*. My son's 156 has a CD in it that came free with a newspaper - they can be found in charity shops. It's been in there years and has completely solved the problem.
May be worth a go ( or a cassette if you don't have a CD player ).
* I do recall reading in the 156 forum that this fix didn't work for one person.