Some vinyl triggering sub to crackle

Thanks guys.  Im leaning more towards Rauls explanation as digital gives to issues at all. I have a new Soundsmith Cartridge coming so hopefully the tech can help me troubleshoot when he comes out to install. 

Do you guys recommend a turntable mat? If so which type or model? I think this might decrease feedback. I didnt want to alter the sound at all but may pick one up tomrw.

Update: voice coil was blown. Replaced driver for $570.00 USD and so far so good. Vinyl playing just fine now. I have to break it in over next 24 hrs with not pushing it hard.  Dealer had a demo for sale for 2500...was tempted...as thats 2K off! Ill wait til spring and offer them 2200...

It may be gone by then. You really need to get a active crossover and stop connecting the subs to the amp. I know that is what REL recommends but they are doing that to lower costs to make their subs more appealing. I just had an experience with a fellow who was using a Parasound Hint Integrated which has a built in subwoofer crossover. H was use in the amps output to drive the subwoofers and was unhappy with the sound. I got him to move the subwoofers to between the speakers and to hook their line inputs to the hints crossover adjusting the crossover appropriately. He says he was blown away by the difference. This was all done by email so I could not listen to it personally.
Trying to get away without a proper subwoofer crossover partially defeats the advantage of getting some warfarin in the first place. But, the subwoofer manufactures do not want to subject the purchaser to the expense of having to buy another 2 sets of long interconnections. They could defeat this problem by providing outboard crossovers for their subwoofers.  To my knowledge only JL Audio does this.  The fallback position is to install the appropriately sized capacitor on the input of the amplifier to roll off its base. This is only first order right better than nothing.