air purging into sump?

ok going to be hard to explain but the flex line that dumps into my filter sock which come from the bulkhead purges air out every 3 to 4 seconds. the top that drains is a t with a 90 on the side of the t and on top of the t is a cap with a hole drilled. its noisy almost like a toilet running and the flex pipe underneath the stand which goes to the sump purges air.... iam at a loss of what to do