I am guessing you are using a power supply from your junk box, not one that came with the recorder, and that is a switcher (most of them are now) and it's a cheap (noisy) one. Ham radio people address by either finding a better switcher or by using a linear supply.
Batteries don't care about harmonics so if your power supply came with a battery charger that might be the reason it's so noisy. In your shoes, I would see if the power supply you have says Marantz on it. If not I would call customer service and find out if they have a reasonable cost replacement. While on the phone I'd ask what the recorder wants to see (voltage and if it's regulated) Then if they want too much $ I would try about a dozen other adapters looking for one with a brand name I recognize and the voltage and current numbers I expect. If the support person says unregulated is fine, and gives a range for input instead of a single value (like 11.6 - 14.4 VDC for example) I'd try a linear supply, I always have one on my bench. Sometimes linear supplies are regulated somtimes not, you really can't tell without scoping the output. It used to be the answer was to find a good cheap regulated linear power supply but those are very rare now. All this works for me because I've known the problem exists and have squirreled away good power supplies for when it crops up. BTW I know almost nothing about migratory birds. :-) But I love monitoring the list. Good luck, Brian -- NFC-L List Info: Welcome and Basics � http://www.northeastbirding.com/NFC_WELCOME Rules and Information � http://www.northeastbirding.com/NFC_RULES Subscribe, Configuration and Leave � http://www.northeastbirding.com/NFC-L_SubscribeConfigurationLeave.htm Archives: The Mail Archive � http://email@example.com/maillist.html Surfbirds � http://www.surfbirds.com/birdingmail/Group/NFC-L Birding.ABA.Org � http://birding.aba.org/maillist/NFC Please submit your observations to eBird! ��http://ebird.org/content/ebird/ --