Version I'm using:
1.0.6.3
Forge Version installed:
1614
Description:
When I have weather2 v2.3.20 installed with dynamic surroundings, I can't hear rain, I think it must be something to do with weather2 when there is a storm.

CleanWeather v1.1.0 for 1.2.5 (for a future dynamic surroundings update).zip
If you want to have a look at the mod file, I've attached a file here

but when I don't have weather2 installed I can hear rain

Yep. Weather2 is in control of rain splashing and what not. https://github.com/OreCruncher/DynamicSurroundings/wiki/Compatibility#weather-2