I have some radio chatter on the download site that is made to add to engines. The chatter stays with the engine, its not just parked on the side. They are set up for 06 but I think could be made to work in 04 with a slight modification to the sound container lines.
They are kuid 39134:100832, 100834 & 100835.
Open the folder and inside there is an instruction folder that explains how to add them to any engine. They do require you to add a sound script container to the config file, which is very easy to do in 06. In 04 you would have to write it in manually. And as I said earlier there would have to be a slight mod made to the lines that I show in the instructions for 04 to be able to read the .wav file. I have not however tested them in 04.