Stinky shower (not from the drain)

We have a 3 bedroom, 3 bath home in Hua Hin. Recently, when I have been using the shower in one of the bathrooms, as soon as I turn on the water, it stinks. It goes away fairly quickly, but it is baffling me. A few details – there is a hot water heater under each sink in the house, and the ones in the bathrooms supply hot water to both the sink and the shower. The other two bathrooms / showers / and kitchen sinks do not smell.

Ideas? Should I take off the shower head and clean it ? Should I try to pour some sort of cleaner down the line after I take off the shower head? Should I take apart the water heater and see if something is in there?

Just to make it clear, none of the other sinks or showers stink when we run water, so I’m thinking it may be pretty close to the shower head itself. But I don’t want to start tearing stuff apart if there is an easier solution that I am not aware of.

Thanks much for any advice.

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