I hate holes in the information provided because one can never take anything for granted in sub testing:
Somebody has to ask:
Is your mike at
ear height at the listening position?
While moving the sub is one option. Another is moving yourself.
Try moving the mike backwards or forwards a foot or so to see if it affects that 45Hz trough.
What is your room size? Room modes can be calculated:
http://www.mcsquared.com/modecalc.htm