Strange noise???? 98 GMC Z-71

[ronorosz]

I have a 98 GMC Z-71. When I start the vehicle I can hear a strange noise almost like a hissing noise in the cab. It is loudest when you put your ear in the vicinity of the steering column at the brake pedal. It disappears sometimes when you put the vehicle in reverse. When I drive forward the noise is intermittent but sometimes constant. It is louder during the winter months. When I apply the brake and stop the noise disappears. When I am driving and turn right the noise disappears. When I turn left it seems to get louder. I keep thinking it is my power steering pump but don't want to start replacing stuff and not correct the problem. I'm scared that's what the dealer will do so I haven't taken it there yet. Any ideas?

[KA9MOT]

Vacuum leak in the brake booster? Just a thought.

[ronorosz]

I took it to Midas and they pulled the booster hose (?) off and the noise continued. The truck drives fine but the noise is a nuisance.

[1fatcat]

Depending upon the sound your talking about, it might be a fuel line rubbing against the fire wall....the engine side of the fire wall.

[TNcarguy]

I've heard some automatic transmissions that would make a noise when it's cold and you turn one direction or the other. More of a whining sound, though. You might try kicking it into neutral when it's making the noise, to see if it stops. Shot in the dark.