AGW Controller

[5050]

i have a couple of the AGW 401 feedback controllers which I find very good and bulletproof in use.  The other day I was testing some locos on my new layout.  Most of these have Mashimas of varying sizes and I became aware that one loco, with a small Mashima, was 'buzzing' even when the control knob was fully in the off position.  I checked the output with a multi-meter and discovered that there was still a small amouint of current being emitted.  Thinking this may have been a fault developing I tried my standyby controller, identical in every way but very little used, and the same was happening.  There is insufficient power being emitted to move the loco(s) but I am intrigued.  Is this a common situation with feedback controllers?  I have been using these AGW ones (and others) for many years and not knowingly experienced this before.  In the general noise of an exhibition it would not be noticed at all but in the quiet of home it is.

 

Any comments?