Hi Guys, for the past couple month I have noticed a noise after start-up that I haven't herd before. It sounds like my fuel pump (raptor 100) is cycling like a two speed pump. The truck starts fine and the noise starts up after about 30 seconds, then it cycles a hi and low pitch sound every 30 seconds or so for a couple minutes then is becomes steady like a fuel pump. I hear a relay switching as it cycles but I can't locate it. I have temporarly disconnected the power to the fuel pump and the noise goes away. I have changed the fuel filters and checked the raptor fuel pump inlet screen, no change. The truck starts and runs fine, I just don't want something to fail and leave me stranded. Is this normal, maybe the alternator is re-charging the batt's after starting and the voltage is fluctuating causing the variation in noise.
Any ideas or suggestions would be appriciated.
Thanks.

 

Could it be your grid heater kicking on and off pulling the amps down giving you different tones on the fuel pump?

 

That's what I thought, so I pulled the fuse for the heaters and there was no change.