Mouldy plywood in kitchen

[Papayalady]

Hello.
I've had a horrid 'cat pee' smell in my kitchen, under the unit where the sink and washing machine both are, since I moved in last summer.
I've had waste pipes replaced, which improved the problem, but it's come back with all of the heavy rain this summer. It's so strong you can smell it when you come downstairs in the morning, or when you walk into the front door (my house is small!). I recently heard that this could be caused by mould on plywood of kitchen units. I haven't been able to move the washing machine to check the wood as I'm not strong enough. But in the meantime, I thought I'd ask to see if anyone else has had this problem and resolved it? Thanks

from what you describe, the source of the water is a drainage problem

Is you kitchen floorconcrete, or wood?

Id there an impervious floor covering such as vinyl or laminate? Can you look under it at an edge?

please take some photos of the waste pipes inside the house, and the outside drains, if any, especially if there is a yard gulley outside, where the rainwater downpipes and the sink waste go. Any signs of sunken, cracked or repaired concrete or paving are especially interesting.