Noise under the dash

[Pfrdthegreat]

Hey y’all, I’m new to the group but not to these trucks. I have A 99 Chevy k2500 Ccsb that I’ve had since new. Just dropped a new crate motor in it in October. I have a new type sound under the dash, like a wurring sound. When I turn The key to the on position, it sounds like something under the dash is priming, kinda like A fuel pump, when I crank The truck I can still hear it. Only inside. Can’t hear it outside. When o shut the truck off the sound continues for a second or so and then quits. Doesn’t seem to be affected by rpms. Any ideas? A few people have said blend door motor but I’m not sure. Thanks y’all

 

[SUBURBAN5]

Hey y’all, I’m new to the group but not to these trucks. I have A 99 Chevy k2500 Ccsb that I’ve had since new. Just dropped a new crate motor in it in October. I have a new type sound under the dash, like a wurring sound. When I turn The key to the on position, it sounds like something under the dash is priming, kinda like A fuel pump, when I crank The truck I can still hear it. Only inside. Can’t hear it outside. When o shut the truck off the sound continues for a second or so and then quits. Doesn’t seem to be affected by rpms. Any ideas? A few people have said blend door motor but I’m not sure. Thanks y’all

With out hearing it it's hard to picture it. Sounds like something electrical for sure. Do you have a stock radio?

 

[618 Syndicate]

See if you can reproduce or change it with the HVAC controls.
Sounds like blend doors.

 

[GM01]

Just checking in here to see if you found a fix yet, I've had the same thing going on with my new-to-me 89 GMC 1500. Coming from under the glove box it sounds like. Old owner was second owner, said it did that as long as he had it too.