i bought an 06 sierra 1500 last august. the 2 front radio speakers haven't worked until this week. the rear speakers always worked great. this week the fronts started working intermittently. also notice the warning chime also works for door ajar,seatbelt not buckled etc. which never worked until the speakers started working. was wondering where i should start first to try and find the problem? forgot to add that the radio is just a plain jane OEM am/fm thanks for any replies.