Strange hissing noise while coasting

[Silverhorn]

Hey guys,

Relatively new to the forum, I took over all the maintenance on the Infiniti recently, and its made me pay extra attention to the car. When I'm coasting, as in no gas pedal or brake, I hear a strange hissing sound. It sounds a lot like the ventilation system is "leaking" maybe. When I apply any gas, or brake the sound stops imediatly. I can't remember when this issue started, but I've started to notice it lately. Any ideas what it could be? I've searched the forum and I can't find any existing info on this issue.

Thanks!

[4xq]

The vacuum booster for your power brakes will make a hissing noise like that if it is leaking. I would probably look there first.

[Silverhorn]

I'll try that and post back. Thanks for the quick reply!

[Silverhorn]

Took it to brake masters a while back and I forgot to post. I coudln't find any obvious leaks and they said that it is probably the master vacuum cylinder that had a leaky diaphram. As the car warms up or is under pressure the sound goes away. He said I don't have to worry about it until I notice a loss of braking power. Can't wait to change that as its mounted to the firewall.