The reasons can be
1. The Particular tyre have a molding defect,
2. The rim of the tyre is wider than actually it should be.
We have discussed this problem earlier also, the rims needs to be good tight match with the tyre.
If the rim width has increased, we may also have to modify the tyres to avoid this problem in future.
If there is a tyre defects, we will be careful. Please send the picture of the tyre without the rim, that will help.
Regards
JAY
Krypton Industries