I have a 1999 Oldsmobile Silhouette the radio is not working properly no sound only when I turn the key back and car off then the sound comes on.

That sounds to me like you have a bad ignition key switch. for it to read the chip in the key the switch needs to be able to recognize it. Hope this helps getting you going again :o)
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It could be, best thing to do is start your car and with radio on, but volume on low, listen to the passenger rear speaker for the noise you are talking about.

if the radio is original
security code .speakers and all other functions work

could be faulty speakers
or an internal circuit board failure

pull the radio out have radio checked
if beyond repair
you could source a used one or fit a newer after market unit

Try chsnging the starter cylenoid

NEED RADIO UNLOCK CODE TO RESTORE RADIO
IPC INOP. SOUNDS LIKE IP CLUSTER IT'S SELF, COMMON ISSUE

Flat battery .. replace it an it will be fine

Inertia swich maybe?????? I hit a pot hole with my car and shut off just had to posh the inertia button in trunk.

please read your owners manual . that code is for anti theft radios the information is in there hope this helps

The easiest way to obtain a radio code for any vehicle is to call your local dealership, in this case a Pontiac dealer, and give the guy in parts dept. the VIN # of the vehicle. Won't cost you anything. Give it a try.

The radio and lights usually work when the battery is mostly dead. Check battery and cables to make sure you have a FULL contact. Also do the same with cables and starter. Most parts stores will check battery, altenator, and starter on bench test or in the vehicle for free or extremely cheap. Also you may want to check starter relay for current with an ohmmeter