Product review (3 stars): Mounting Fixture "O" ring worn
Main problem with this filter is the "o" ring on the "pointed" water release valve in the mounting fixture that attaches to the wall.  This "O" ring deteriorates over time.  The filter will hammer or have greatly reduced output.  There is not a spring on the valve, but it is kept closed by water pressure until you seat the filter.  The nubs on the filter activate the water release valve.  A worn "O" ring will not release completely and the filter will have reduced or no output.  Just replace the complete fixture.  The cost is basically the same whether you replace the complete fixture and filter or just the filter.  I put in a new filter about 1 month ago and the fixture just started hammering today.  Figured out it was not the filter, but the mounting fixture.  I tried the garden hose washer and that did not work.  Finally just bought a completely new assembly.  I used the old filter and everything is working fine.  It was not the nubs on the filter, but a defective "O" ring on the valve where the nubs contact.