In my 2005 Chevy Cobalt front speakers went silent (ones in the back still work fine). What could be the reason and what's the best way to fix them?
Did you buy this car brand new? It is possible that someone traded it in and did a hack job putting the speakers back in. A previous owner could've potentially had an after-market stereo.
I assume your stereo is factory?
If the connections to the speaker are ok then you may have dirt in the cones. I had a speaker stop working because of that. As soon as I started looking at it carefully there was a ball of dirt that stopped the cone from moving at all. Once I cleaned it up it worked again like new.
Since you say that the speakers will work if you jiggle them I imagine it's not for lack of a good connection to the radio, but if nothing else works this might also be worth checking...
Another quick check is to swap one of the front speakers with one of the back speakers and see what works and what doesn't. This will tell you if it's the speaker or a bad connection.