High pitched squeal from C64 when turned on

[eight088]

Hi all

As the title suggests, I'm getting a high-pitched squeal from a c64 when it's turned on. It's not the monitor/crt, as the same monitor hooked up to a different c64 doesn't make the noise. Suspecting the SID chip, I removed it and the noise goes away. I put a different SID (from the c64 that doesn't squeal) and I get the same high-pitched noise from the monitor. Any idea where I should be looking?

Cheers

 

[eight088]

Just an update, when I touched C13 the noise went away. I replaced the cap but the noise was still there. I ran a bodge wire from the output of c13 to the audio out on the DIN connector, and it seems to have fixed it! Easy fix!