BMW: Electrical, voltage spikes, electronic gadgets

Question
My radio and time display seems to be blinking faintly(I have E30 model). I took the following tests:
Battery Voltage (Engine OFF)= 12.50
Battery Voltage (Engine Running) = 13.38 - 13.72
This reading justs jumps all over the place. I took a similar reading off another car and the battery voltage reading with the engine running was very steady.What can I do?

Answer
Pete,
 Just to clarify the problem:  So your radio is blinking/flickering because of voltage spikes or inconsistancy?  

 If that is the problem, do you have any accessories in the car?  Such as big speakers, or an amplifier?  Any other electronic gadgets in the car?  If you have an amp and speakers then this will use a considerable ammount of energy when the bass is produced in the speakers, this can cause the headlights to dim and voltages to be irregular.

 If you have nothing in the car to use extra energy, and your lights are flickering then the alternator "could" be at fault.  I have owned several E30's and I've never come across this problem (yet).  How long has it been since you've replaced the alternator?  The Voltage regulator on the back of the alternator could be going bad.  You should be able to pick up a Voltage Regulator at local parts stores and just replace this.  It shouldn't be very expensive either.  If the Alternator is several years old, it's probably best to just replace the whole unit.

 I will check around on some forums to see if anyone else has had these problems.  If I come across anything I will post it here.

 Hope this helps,
 Josh