in the door trims .. this is what i found to be most probable ...
1. if the speakers have not been put in tightly.
2. theres this little handle thing that the door trim sits on, this usually goes loose after a while, haven't figured out a way to keep it perfectly tight ... i might try putting some tape between the handle and the inner panel. even tape the whole handle thing to add a bit more weight to it as if you're sound deadening it .
3. when u remove the door trim u will see some of the plastic screw holder thingies will be pretty much farked ... go out and buy some new ones from the nissan dealer ... costs about 30 cents or so each ... replace the farked ones or the half farked ones with the newer ones.
4. if ur insane then go out and buy some sound deadener, i havne't done this as yet as i'm pretty lazy, but will do so soon.
let me know how u go.
i've got this annoying sqeakin coming out of where the stereo is, i'm pretty sure its the emty din comparment since i broke the spring mechanism and it doesn't close by itself properly, so i'm going to replace that soon.