You can get rid if it...see below. have had 5 or 6 69ffb4's that have had that problem. After doing everything I can, including sending it back to ranger twice, I now just tell people if the problem and the ones that want echo, I buy the echo board that is used in the mirage 86 hp because the board and the knob are all in one and it installs easily on the side.
Any way, you can get rid of the hum by adjusting the echo delay. The problem is you have I adjust it to the point that the delay is so long that you'll never use it. So, obviously that's not a good resolution.
Have the se problem with the stealth PRO.