Hi all! I'm an old retired guy on a very limited income so I have to fix things myself. Anyway, we are living in a house with a PEX plumbing system here in southern California and recently every-time someone flushed the toilet, we could hear a faint 'knocking' or 'pulsing' or 'pumping' sound. We have been here over 9 years and never heard the sound until the last few months. In the last few days the sound has gotten 'louder', and it now appears to be happening even when the washer machine goes on. I have read a few posts about air hammer even in a PEX system, and I know that somewhere there is a 'manifold' that distributes the water to all the faucets, sinks and toilets, but I have not been able to locate it. I am thinking the Manifold is hidden somewhere in the attack because it is easy to tell it is no-where in the garage. Don't see any obvious leaks anywhere but since the sound is louder and more pronounced now I hope it isn't getting worse? Can anyone offer any advice on what to check and/or look for? And what to do about it. Thanks in advance to all who offer help and advice!