It was perceptive of you to notice that! It sounds like the compliance of your cartridge, and the effective mass of your tonearm, are not optimally matched, resulting in the combination having a resonant frequency in the "warp region" of typical records (a few Hertz). The following writeup provides a good explanation:
http://www.audioasylum.com/cgi/t.mpl?f=vinyl&m=793257
Regards,
-- Al
http://www.audioasylum.com/cgi/t.mpl?f=vinyl&m=793257
Regards,
-- Al