There's no need to block T3 users. Just be aware of problems that some audio files have from 'some' of those sources. If you see search results for audio from T3 sources, then if you have alternative choices choose those or else just make a note of the file size v's bit-rate (mp3 quality setting) so it looks ok. If you see different results with same bit-rate but different size or vice versa, then you know there's something wrong with the file. And the culprit will most likely be the T3 source. So choose the other in that case. Remember that not all T3 sources are bad!