that may be because it is sucking air while it is running. you said the leak was near/at the skimmer. when the pump runs it sucks water into the skimmer and through the pipe to the pump then pushes it through the filter and out the return. if you have a drip at the skimmer area where water goes out some smalll hole passively, and it stops when the pump runs, it could and is very likely to be sucking air through that same hole that leaks water.There is no leak when the pump runs. Dry as a bone.