Originally Posted by humble_biker
Are there little "blow off" holes on the inside of the rim near where the vertical part meets the horizontal part? Often times if these little holes are present and depending on the quality of the tube they can be the fault. (Sorry for the weird description) If this is the case cover those holes with a wider tape or change to a heavier weight tube.
I'll have to check that when I get home. You mean right where the sidewall of the rim meets the part that the rim tape is applied to (sorry I don't know the correct names either)?