Amtrak P40 Noise - what is it?

When I listed to the Downeaster pull away from a station stop I hear a loud "whirr" noise as the locomotive reaches around 5-10mph. It sounds like a motor rapidly spinning up, but the locomotive is already moving. What is it?

I'm pretty sure the downeaster is being pulled by P40/AMD-103 locos.

Thanks.

HEP generator, maybe?

Probably the equipment blowers kicking in to provide cooling to the traction motors. No need to provide cooling to the TM's when your standing still.

It comes from the Prime Mover it is a clicking sound.

They don't use P40's however but P42's, only P40's in service are on MNCR.
The whoop sound like submarine alarm is aircompressor starting, only thing I can think of is the Equipment blowers.