1997 toyota 4 runner, stereo system

Sounds like you have a shorted speaker. Disconnect one speaker (both positive and negative) and listen to it. If the problem goes away then that speaker or wires leading to it is your problem. If the problem does not go away then reconnect that speaker and disconnect another one. If you have a shorted speaker this will quickly lead you to it. I have also seen more than one installer in my time pinch a speaker wire on the metal mounts when reinstalling a radio in a Toyota. Be sure that this did not happen to you when you put your radio back in the last time.