If a thump occurs on multiple LP's precisely once-per-revolution, the cause must be in the rotating parts of the table.
It might be an uneven spot in the platter or matt, a worn spot on the bearing, an anomaly in the drive system or motor or anything else that rotates. The only way to know is to investigate the various possibilities, which only someone with access to the table can do. Consider this an opportunity to get to know your rig a little more intimately.
That said, from a practical perspective I second Dan_Ed's advice. Whether you find the problem or not, turn off the sub (which is a free way of providing a LF filter!). While some LP's do have notes below the 35-40 Hz rolloff of your Thiel's, the B&O rig won't reproduce them well enough to be worth worrying about. When spinning vinyl, your sub is likely to produce more mud than music.
