05 Escape, started as a high pitch noise, evolved to a hissing noise under the dash, stops when brake is applied, then gradually returns. No performance issues with brakes or engine. Any thoughts???

 

It's a leak in the center rod on your brake booster. Went through that experience on my 01. It will probably do it intermittently, but it will keep happening. You can try spraying some Silicone spray or WD-40 whatever you have handy, down the center shaft from the inside, may stop if for a bit, but the cure is to replace the brake booster. If your mechanically inclined the booster is not too hard to replace, probably maneuvering the booster out of the engine compartment is the hardest part, and being a contortionist working under the dash of your Escape. About 1 hour job if you do it yourself. I got a brake booster from local parts store in the DFW are for $100.00

Take Care,

Scott

 

FYI, Here's a tip if you do replace your brake booster. Remove the brake light switch and cruise control cut off switch before you start to do any removal of the brake booster. They are under the dash one is gray plastic the other is blue plastic. They just twist one direction (I think counter clockwise) and pop out. Otherwise you might pop the brake pedal back, toward the rear of the vehicle when your removing the connector to the brake booster and force the plastic plungers on each part to collapse into the part and breaking them, (hmmmm.... wonder how I know that ;o). It will save you from having to go to the Ford house, or in my case the salvage yard to get replacements.