I forgot to say that there are no other problems other than the sound. The car is running exactly the same as before the sound started.

I am thinking it is something in the vacuume pump. Is it even possible for it to make a loud tapping noise?

Thanks,
Stephen

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85 300D 305K miles WVO(105K so far), Mine
82 300SD 235K miles BIO-D, Wifes
96 F250 SC PSD 4X4 285K MILES BIO-D, Ours
89 BRONCO 182K MILES sold
Finally Compression Ignition Only!