fm bug

Hello, A week ago I bought an old volvo cr 905 headunit. But I am encountering a weird issue. When I play cassettes or cds the radio works flawlessly. But when I play FM radio it works but not good. The first 5 minutes the fm works good but after that it starts to stutter and lowering volume...

hey guys i,m new to this forum and Lt spice I am planning on building a FM bug using hardware, i am trying to simulate this circuit using LTspice In simulation i am replacing the microphone with a voltage source of 10mV and 2kHz then removing 68k resistor. simulation file is attched.Kindly...