Is there an issue with the plug on the Sennheiser ME3 microphone?
Potentially. The microphone as traditionally manufactured by Sennheiser has a unique plug which is designed to lock onto a belt-worn transmitter. This locking ring on the plug interferes with an adequate connection when used with standard audio jacks (see upper plug on image to the right). If you purchase an ME3 from a large retailer, it will almost certainly be one of the standard ME3 microphones with the unusual plug and you may have troubles making an adequate connection with your sound card.