Harmonic feedback when recording?

[ACfireandiceDC]

Hi.

I'm recording a song on GarageBand, and I'm mic-ing the amplifier until I get an effects processor. For my equipment, I have:

-A Samson dynamic microphone
-A Line 6 Spider IV 30 amplifier
-A Douglas Hadron 725. I recently had its action lowered, in case this may have an effect.

When I play anything on the low 'B' string, I hear a harmonic-like noise when it comes out in the recording and it's very frustrating. This does not happen on any other string. What may be the cause of this? Is there something I can do to stop it from happening?

 

[Metal_Webb]

Try tying a hair band or the like around the strings behind the nut. There will be resonances there if the section of the string isn't dampened.