QUOTE=skilsaw;12303286]My guess is the tube is not seated correctly in the rim. Examine where the tire and rim touch. Look for a bit of the tire that is pulled out farther than the rest of the tire.

Let the air out of the tire,
massage the high spot on the tire down into the rim.
Confirm that the tire isn't pinching the tube anywhere.
Inflate the tire.

Good luck.[/QUOTE]

+1. Most likely cause.