I've found that inexpensive mic "extension cables" for long runs (anything totaling 10 feet or more) can turn into antennas and pick up all sorts of radio frequency and electromagnetic interference (RFI and EMI, respectively). This could be a 60 cycle hum for AC power cabling or florescent lights or incandescent lights on a dimmer switch or other RF equipment being used where ever you were recording video.
The Azden SMX-10 was designed to be used when mounted to the camcorder. I presume there is no extraneous noise when you do that (and don't use the extension cable).
When you add the extension cable, there is noise. That tells me there is an issue with the extension cable. It could be anything from poor quality connectors or workmanship to the RFI/EMI mentioned.
When the professionals need long cable runs, they use balanced cables - they are shielded. They also use XLR connectors from the mic all the way through to the camcorder.
I use shielded cables with my mics and camcorders and have not had the problems you report. These cable runs have been as long as 70 feet.