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
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
Anyone know what could be causing this sound? It only knocks when the
AC is running. The cooling power of the AC doesn't seem to be affected
by this problem.
Before I shut off my vehicle, I always turn off the AC and let the
vent run. The knocking will slowly stop over the course of about a
minute while the vent runs. Then when the vent is blowing warmer air,
I don't hear the knocking sound at all.
Any help would be great.