High Frequency Noise/Whistle in Background [SOLVED]

I am using
Win XP Pro, Audacity 2.0.5, .exe version, and Soundblaster Play! USB soundcard. 48KHz (native sample rate) 32bit recording.

There is always a high frequency noise/whistle in the background when recording, even when the mic is turned off or unplugged. Strangely the noise is not there when listening to the Microphone live through the headphones.

I’ve attached a sample of the noise where I have only attached the 6.5mm to 3mm adaptor plug to the mic port, but not attached any mic.
Please advise on why this might be happening.

It is most likely the adapter itself.
I had the same problem and an exchange solved the problem.
try another 3.5 mm jack–it can even be a head phone or ear-pads.

It seems to be something to do with my room. When I take the laptop out into the living room and do a recording the noise is gone. I wonder if it is because my Pocket Wifi is in the room. Anyway, for now the problem is solved.

Yes perfectly possible. Any source of electromagnetic interference ( Electromagnetic interference - Wikipedia ) could cause it.

I marked this as [SOLVED].