are you sure its from the dash? have you checked the engine bay? I have doubt na under the dash kasi nakapagkalas nako ng dash ng frontier (both standard and elite)...walang item duon na prone makalas/lumuwag and create a rattling sound.

Sa engine naman meron tok-tok-tok sound pag maluwag ang rocker arm ng valves. Maingay ito sa cold engine (kasi hindi pa lubricated ng husto ng oil). Pero pagbumagal ang takbo hindi ito ganun kanoticeable.

In case you want to open up the dash...the quickest way is to remove the glove compartment muna and then the "face" cover ng a/c and radio. The face is the trickiest to remove...specially sa elite.

Sa driver side madali lang tangalin (2 or 4 screws lang).