If moving the turntable and/or subwoofer does not work, your cheapest option, as others have pointed out is to install the KAB RF1 subsonic filter. However, this will require that you insert the filter in between the phonostage and the amplifier and will require an extra set of RCA cables. If you are using XLR connection from your phonostage to amplifier, then it becomes a little bit more cumbersome and will require xlr to rca converters (male and female). The RF1 filter can also be connected directly to the tape-loop if your preamp/phonostage has this option.
Other options include getting an isolation platform like HRS, SRA or Minus K depending on your budget. And if all else fails, then get a phonostage with a built in subsonic filter.
As an fyi, I had subsonic issues from my very first turntable, likely due to my suspended wood floors. In the initial stages, I did have to replace the driver on my REL subwoofer. Subsonic rumble can lead to equipment failure over time if not mitigated properly.