may have a hole in it where it has chaffed on something? or may have a submerged pump in tank that is faulty,are you checking supply pipe and not return pipe.unusal to have the pipe blocked, if anywhere it could be in tank/tank unit where outlet pipe is.try following pipe back and check for damage/places where it might be drawing air.
k
November 2011
howtomendit.com for free repair help, information and advice.
