I have one mp3 that gives a click at the same point each time.

This is a faulty MP3, for instance, it probably has a section of corrupted data that is missing the correct frame headers. Or maybe there is a clump of ASCII garbage data in the middle of the file somewhere.

Different decoders will interpret MP3 errors differently. Some will click, others will have a "dip" in the sound, etc.

To check out your MP3s for errors, click here.