Culligan Filtered Drinking Water Smell

I recently installed a Culligan Tri-valve filtered drinking water tap. After about one week, the filtered water started to smell of sulphur/bad eggs. Changing the filter cartridge made no difference. I have used a "stand-alone" Culligan filter tap for a number of years without problem.
I contacted Culligan aftersales who advised me that the smell could be caused by a reaction with the rubber seals within the tap itself and that they recommend that I swap back to using the old tap!
Has anyone got any suggestions on what can be causing the smell - could it really be the rubber seals? Can I do anything to remove the smell?
I do not really want to have a standalone tap - can anyone suggest alternative brands that offer a tri-vale style tap?
Thanks, Steve
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