I have five MX395B-BI-LED microphones that hum and buzz whenever there is an A.C. power cord placed near the mic. Any ideas?
There is likely an erroneously attached date code label inside of the mic housing tube, positioned exactly where the 5-pin XLR connector ground tab should contact the metal mic housing. This label disrupts the ground path and the result is audible hum/buzz.
To correct the problem in the field: Loosen the XLR set-screw, carefully slide out the circuit board, and scrape the date code label from the inside of the tube. While the circuit board is extracted from the tube, the low frequency roll-off DIP-switches can be adjusted if desired.
As of August 23, 2012, this manufacturing error has been noted and corrected in the MX395 models.