I used to get this on my old cheaper wheels but not on my current ones. I'm sure you're not riding cheap wheels of coursebut I guess just some do and some don't.
Maybe it's the tyre not sealing 100% against the rim.
Had it on two different tyres neither budget.
R500 training rim & H plus son rim both do it.
Don't ride my carbon rims in the wet if I can help it!
but I guess just some do and some don't.



