I have a 2007 Ford Escape Hybrid. When running the AC, I hear this knocking sound coming from under the dash on the passenger side. It sounds like some kind of valve opening and closing quickly, over and over. It isn't continuous, but it will occur at least every 10 seconds. It might knock 2 or 3 times, then not at all for several seconds, then once again, and nothing for several seconds, etc. I think I found the device making the sound. I can feel the vibrations of the knock coming from this device under the dash on the passenger side:
Any help would be great.
Thanks!