I've got a standard 2006 380 SX audio system. The right hand speaker gives off a noise like a frog croaking when some music is playing. Any idea what this is and if it is a speaker can you get to it easily? I assume this won't be covered by the factory 5 year warranty.

You've blown the speaker. Get aftermarket speakers fitted, problem solved.

If it turns out that they are indeed blown and you decide to add aftermarket ones don't hesitate to contact me and I will be happy to supply you some.