Does anybody have a problem of viscosity and clumping solution during Jurkat cell lysis with RIPA buffer?

I'm trying to have a good concentration of a supernatant from Jurkat cells. I've lysed 5 million cells in 500 ul of RIPA BUFFER (almost standard RIPA I would say) and it was already sticky. Than I sonicated (3 times 30" and ice in between). Still on the same situation. Then I tried to pellet it 12000*g 20 min but I was able to obtain only 200 ul from the total amount.

Any advice?

Thanks
Giuseppe