Strange low frequency noise when playing vinyl.

I'm getting a strange low frequency noise when playing vinyl that I did not notice until a month or so ago. My turntable is a Scoutmaster with JMW9 tonearm. I've included a link to a recording I made of the noise. I used the locked inner groove of an LP and removed the belt from the motor and spun the platter by hand. As you will hear, the noise will change with the speed of the LP. I have tried the following the remove the noise: Two different cartridges by different manufactures; outer ring, no outer ring. Clamp, no clamp, two different phono stages. Only possibilities I can think of is bearing noise or resonance of the tonearm.

Link: http://www.mediafire.com/?iski6xsvdsbwbq7

You may need to turn your speakers up to hear the noise.
A_L