After publishing my initial review of the Sangean ATS-405, I received feedback from several ATS-405 owners (via comments and email–thank you!) who do not have the internally-generated DSP “birdies” that plague my receiver on 800 and 1600 kHz AM. I strongly suspect my ATS-405 has a manufacturing defect of some sort.
Sangean is kindly sending me another ATS-405 review sample for comparison purposes. I will post an update to the initial review as soon as I’ve had the opportunity to evaluate the new sample.