Solved! High Pitched Noise from Speakers

Solution
If the noise is the brief tone that is heard for a few seconds in the recording it doesn't sound like a ground loop but could be an oscillation.
If it doesn't happen with the preamp not connected to the amp it is in the preamp. Try it with a source connected to the selected input since RF can get into a preamp through an unused input.
If it happens when the amp and speakers are the only connected components then it's in the amp.
If you can try another preamp (or connect a source with variable output) directly to the amp) you can isolate the problem. Try a different cable. If the amp has a 3 prong AC cord try using a 3-2 adapter to lift the ground.
If the noise is the brief tone that is heard for a few seconds in the recording it doesn't sound like a ground loop but could be an oscillation.
If it doesn't happen with the preamp not connected to the amp it is in the preamp. Try it with a source connected to the selected input since RF can get into a preamp through an unused input.
If it happens when the amp and speakers are the only connected components then it's in the amp.
If you can try another preamp (or connect a source with variable output) directly to the amp) you can isolate the problem. Try a different cable. If the amp has a 3 prong AC cord try using a 3-2 adapter to lift the ground.
 
Solution