I just installed my stereo system on to my car a few days ago and I get this ticking
sound transmitting thru my speakers when my cell phone has bad reception or when i'm on the phone (Nextel)
Never happen on the stock radio. Would it help if my RCA cables were shielded?
I'm not even sure if it is or not.

 

nope, welcome to nextel, it is common, its the radio frequency transmitter for the 2 way, it will also happen on desktop radios, tv's..its rather annoying. the reason your stock radio didnt have it is becuase it didnt use RCA's at all. your aftermarket one does. even some radios like my i730 is so powerful it affects my nissan car's stock radio.