{Collins} KWM-2 VOX-Rcvr Audio Feedback Problem

I have an early wing-emblem KWM-2 that has a strange VOX problem.  When the VOX gain is advanced, there is low-frequency, pumping, audio feedback in the receiver audio.  The problem seems to be the worst just after the radio is turned on and goes away somewhat as the radio warms up.  Any ideas?
Thanks and best wishes,
Jim Jorgensen, K9RJ

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