[TR] TR3 Howling Noise

[William Brewer]

     So today my TR3A starts to make a howling noise from the engine somewhere. It sounds like someone blowing over the neck of a bottle, but more high pitched. It sounds like it is coming from the left side of the engine, but I am not sure. It is pretty loud and can be heard at idle but appears to diminish with speed.
     I am in the initial phases of troubleshooting. I fear that it might be a spinning bearing or something. I'll run a stethoscope around to see if I can find a general area. 
     Any suggestions on troubleshooting?
     TIA,

     Bill in Tehachapi