There is some relay or something, sounds electrical. Its a 99 4.6. Got it last year and did this occasionally last winter but not as bad. Seems to only do it when its cold, mostly when using turn signals, brakes, and occasionally acceleration.

 

Is it doing it when you're pushing on the brake? Sounds like the brake pedal pivot needs to be greased.

 

No, it also does it sometimes when I accelerate or use turn signals. It won't make the sound when the truck is off and I press on the brake, only when its on.

 

Get under the dash a check have someone turn on the key with a noise that loud you will be able to find that real easy if you need get a stephascope at a local auto store I've heard relays make noise but not that loud let us know what you find iam curious lol

 

Read the info that I posted here
https://www.f150forum.com/f6/98-clic...er-dash-62543/