Buzzing Heard In Speakers
 

'87 300TD

Recently, the above vehicle has been buzzing through the stock stereo. At the lower frequency of the FM it is worse than the upper end. After ten to thirty minutes the buzzing suddenly fades out and does not come back until the next time I start the car. Though I suspect something is up with the alternator, I am not certain this is the only culprit for this symptom. Advice is appreciated.
Steve