Is rattling in rain effective or not

If the bucks are up and looking I don't think rain would make much difference

I didn't know if it being damp would hurt the sound

Not sure about that. I'd say give it a go but be aggressive and loud.

Rain isn't a factor for the bucks...

I decided to try and rattle a little today. Before today I had only rattled a couple of bucks in, never at the same time. I don't know what was different today, but I rattled five bucks in all at the same time. All were young, one nice 8 that looked to be about 3.5. He eventually chased the other four off, then he left. A doe came in about twenty minutes after they left, and he came in hot. Needless to say, it was a cool hunt.

The key to rattling being effective is buck doe ratio and if they can hear it at the right time of year.

Light rain they can still hear it. Anything more than that probably not unless they are very close to you already.

Here's an interesting article on rattling.

https://www.qdma.com/articles/10-tips-for-rattling-more-bucks