My dc return pump has started to make a pulsing sound , its vibrating but in pulses which is confusing me. Ive opened and reset the impeller but no change it didnt look damaged. The water flow out the pipe back into the tank is a constant flow so the actual water flow isnt pulsing just the sound. The sound also randomly gets louder and softer at times though that may be me geting used to it not too sure. The return pump is attached to my uv by vinyle tubing which isnt vibrating or touching anything. The actual pump is whats vibrating. I am very confused as to why its a pulsing sort of vibration and not just a constant buzz. I tried to get a video but the sound isnt coming through over the sounds of water. Any ideas would be appreciated its a great white 3000 dc pump. I only have it running at about 4 out of 20 settings.