My 2001 national sea view loud noise before starting rv help

[Love2RVmore]

So i just went from a 1996 winni brave to a 2001 national sea view 8311 and its great! So much bigger and a great ride.
So i noticed when i turn the key to start the rig this loud noise noise coming from under my dash/steering wheel area. Its the
Last key position before you actually turn over the ignition. Than as you turn the key to actually start the rv noise quiets down and that the truck starts fine.
Also today i pressed the brakes while noise was going and it seemed to quiet down the noise but not fix it. Is this normal. Amy ideas or anyone have a similar rv.

[wolfe10]

As you can see, without chassis information, you will get a lot of answers that do not apply to YOUR coach.

Yes, please tell us what chassis you have so we will be able to better help you.

[jplante4]

I have a diaphragm vacuum pump under the dash for the heater controls that starts when the key comes on.

[jerseyjim]

most likely the power brake brake booster...if you have your foot on the brake pedal when starting.

My 2001 Dolphin does that.......I guess when the motor is running, the noise is still there when you press the brake pedal, but you can't hear it.

[MrWizard]

some Dps have an electric hyd pump for power steering and brakes

[ArchHoagland]

What engine/chassis?

[MountainAir05]

the noise where you press the brake pedal is the Hydro Boost. I do not get the sound unless the brake pedal is push. Sounds like a leaking seal.