Seeburg M100C sound issue

I am occasionally getting a high pitched "whistle" sound from my speaker between the time when a record finishes and is being returned to the magazine, and when the next selection just starts to play. I believe this is suppose to be the interval when the "mute" circuit is activated. All the caps have been replaced and the box has performed without any problems for months up to this point. Could this intermittent whistle sound be due to a bad tube? Thanks for your suggestions. Steve.

Steve,
Since you did not specify which amp is installed in you C, here is a general list of what it "could be"--
Poor connection at: the cartridge, tone arm wires, input plug, any tube, squelch plug.
Bad tube, resistor, or cap ("new" or not !)
Poor contact at squelch switch --or-----The C is looking out of your window, and seeing a pretty girl pass by--Ron Rich

Hi Ron,
Thanks for the suggestions. The amp is a MRA3-L6, receiver is a WSR5-L6, original Seeburg red head cartridge. Sorry I left this information off the original post. I'll work through your suggestions and hopefully identify the issue. Thanks gain. Steve.

Steve,
You are welcome--note: the last "suggestion" is probably the most important !
Ron Rich