Pressure problem?
 

Hi Folks,
Need some help with my 86.5, while driving down a canyon, a sort of hissing sound, more like the sound you get when sucking fluid through a straw mixed with air could be heard from the dash(?). As I would brake the sound would diminish but start up again when I came off the brakes and or accelerated. It pretty much was like this the whole way down. When I got out of the canyon I opened her up and it went away. Could it be a pressure issue from being in the canyon? Or is this a possible serious brake issue???:confused:

Vacuum leak. Check that all of your HVAC settings are working properly. In other words, move the HVAC controls and make sure that the various flaps are opening and closing with each setting. The hissing you're hearing is probably one of the rubber diaphrams leaking. The vacuum pressure is probably changing with engine speed.

If it's not the HVAC controls, check the rubber boots on your intake. They can be pretty loud when leaking air.

Hope that helps.