Next time you change your fuel filter, dump a can of Seafoam in the gas tank a few days beforehand with around a 1/4 tank left. Run it a couple days then change your fuel filter. Drain the filter housing completely, fill it up with more Seafoam, install the new filter, run the engine for 5-10 seconds to get the seafoam into the injectors then let it sit for 20-30 minutes. Fire it up and rev it up to 2k RPM or so for a 30 seconds and shut it off for another 20-30 minutes. Then fire it up and rev it up for several minutes. Take it for a spin and put your foot on the floor to get the junk out. I did this last week and the knock is gone for now and she runs much smoother. At about $6/can it is a cheap fix. I plan to do this for every fuel filter change now.