One day not long ago I began noticing that if I de-tune an AM radio to the upper carrier edge of my 1550 kHz transmission I distinctly hear a "tick-a-tick-a-tick-a-tick-a-tick-a-tick-a-tick-a-tick-a-tick-a" that just goes on and on without variation.
There is no hint of this ticking sound on the center-tuned main-carrier nor on the lower sideband.
The transmitter is an AMT3000 from sstran(dot)com modified to work with a hand-wound loading-coil and Wintenna (metal window in-line with half-indoor half-outdoor vertical antenna ground clamped to basement I-beam below the floor.
Turning the transmitter audio control to zero the ticking sound stops, therefore suggesting that the sound is introduced from the 25-foot audio cable which runs from a computer audio output to the transmitter audio input.
Sending silence from Winamp over the 25-foot audio line results in the same ticking sound.
By software-disconnecting the audio feed from the 25-foot audio line does not change the ticking sound.
Viewing the silent carrier on the spectrum analyzer shows no artifact produced by the ticking sound.
The ticking sound is not interfering with another station because it is not far enough out on the side-band to reach another channel, it's in the "splash-zone" of the main carrier.
The ticking sound is not causing an actual problem... it's just "there", but naturally I'd like to discover what's causing it to happen.
I'll be examining it from time to time, but also seek your input about what might be taking place. If it happens to me it could happen to others, so we need to establish a "cause-solution" file.