Junior5.0

I have a 91 Mustang GT and when brake or accelerate I hear a loud humming noise coming form the engine. What could cause this?

jwog666

is the engine running? lol in all seriousness, its pretty hard to daignose a noise over the net, let alone a noise described as vaguely as this.

mjr46

video...........possible power steering fluid low, air pump or idler pulley and or tensioner pulley on the fritz, possible alternator issue.....ect ect....

88 orangepeel notch

Welcome to the forum Junior, glad to have you.

But as said above, trying to diagnose a humming noise through text is a little difficult. What would you compare the noise to ? Is it at all speeds, or just certain steady speeds ?

Junior5.0

The humming starts after the car has warmed up and is coming from the cold air intake.

88 orangepeel notch

Does it sound like a slight whistle at all, or an electric hummmmmm?

dawson1112

What brand air filter do you have in it? When was the last time you changed the air filter? It sounds like it might just be a piece of the air filter vibrating as the air moves across it. It could even be a little bit of crud built up in the throttle body, or even a slight leak in the fittings of the cai system.

yurizx6r

It could even be the IAC adjusting to much or too little from a vacuum leak. The IAC's will whistle when they are in the extreme one way or the other. But it's hard to tell without more information like everybody else is saying. Is your idle good? Does it get better or worse when you turn on the a/c and such?