[MrFixr55]

Hi Bridkarl,

Sorry that you are having so much trouble with this.  Can you post the complete schematic?  It would be very helpful in helping you with this issue.

You already established that with the volume control full CCW, there is no motorboating.  When does the noise start?  At the first discernable volume control above full CCW?  Quarter turn? Half turn? etc.??

Try this to divide and conquer:

• Pull all the tubes from the 1st RF Amp all the way to the detector, leaving in only the Audio and rectifier tubes.  There should be no noise other than maybe slight hum that increases with the increase in volume control level.  If bad, troubleshoot the audio and power supply circuits.  
  
• If the above test passes, plug in the detector tube and repeat the test.  There should be no bad noises with the volume control set high.  If good, add the second IF tube.  Evaluate.  
  
• If good, add the 1st IF tube.  Evaluate.  
  
• If good, add the mixer.  Evaluate.
  
• If good, add the oscillator (if it is a separate tube, and so on and so on.  Whatever tube causes the noise, troubleshoot the stage.
  

IF there is a BFO (Beat Frequency Oscillator, used to receive CW code transmissions, ensure that it is off or disabled.),

+1 on what Arran states.  A common cause of motorboating is a bad "bypass" cap. This is a cap that is placed on the "load" end of a resistor connected to B+.  The other end of the cap goes to B-  The purpose of these caps is to ensure that there is no "coupling" between stages through the power supply.  Another cause of motorboating is "lead dress" for the input to the audio amp.  This is especially true if the 1st audio tube has a grid cap.
Another cap that can cause trouble is that cap between the AVC line and chassis ground.  This is generally about 0.05uF.