Do you have another source, other than the TT? If so, do you have the same woofer behavior using the alternate input source? If it's only with the TT, maybe you are getting mechanical feedback back into the cartridge due to poor isolation from the heavy bass.
If you are having the same issue with all sources, you have a couple of possibilities.
First, perhaps you are really over-driving the speakers. Your speaker specifications show a frequency response of 50hz - 26,500hz. They don't appear to be a speaker designed to produce a lot of bass. If you turn down the bass boost does the problem go away? Maybe you need a different speaker that is more appropriate for your musical tastes.
Next, you could be sending your amp into clipping trying to get the loud bass you desire.
Either of these 2 possibilities are not good for your speakers. You will likely damage the speakers if you keep doing this.
Another possibility is that your SX-1050 is broken and is sending a bad signal to the speakers. You could test this by inserting a different amp into the system.