speakers pulsate with no bass added

I dont know what the problem is but when i turn my stereo upwithout any type of bass my subs and rear deck speakers start movingin and out slow then fast, But i am not putting any bass in them.I know this is bad for my system so i woul love it if someone was to point me in the right direction please.I have a Rockford fosgat rf9400 cd player cadence 15" mallet subs and now i'm on my second amp to try and fix the problem but it still exists.No wires are crossed and rca's are on right side and power on left, Groung is perfect.john

sounds like a problem with the installation, check your amp's ground, matter of fact, ground it somewhere else.  if that doesnt work, check the ground for the radio....try to ground that to chassis rather than just connecting it in the harness.   we know its not the amp bc you switched them out and still have the same problem.  if you still have the problem, connect the remote wire to the red ACC wire in the wiring harness.  and if you still have the problem, then i would say either your RCA's need to be replaced or the radio is giving you the problem!