weird engine noise

[SAINTLUEY]

each time my car is stopped it makes like a light horn noise (constant) when i have the car moving its fine, what could this be?

 

[02LSE96LSC91SE84TC]

My folks 2000 Cougar does that, we think its the mass air sensor vibrating or something, we haven't been able to solve it. Theirs goes away when it warms up. I'd like to know too.

 

[95ltc]

I think my fan is making noise only when im stoped, but just for a minute or so, and not when im moving.