Some users have reported an internal beat tone that appears every 10 KHz, when operating in the range of 20-21.5 MHz. Apparently the RV terminal switch unit H is being affected by the 1st loop of the PLL unit.
The cure is relatively simple. Add a .01 µF 50V disc ceramic capacitor on the RV line of switch unit H as shown below.
Time required for this modification is ½ hour or less.