Could be a resonance thing..maybe bump the pressure up or down 20psi and see what happens. Sometimes funny things happen with flexy forks that can be..unnerving. I'm looking at you Kinesis!! Or poor geo..
It's going to have to be up - when I rode through at 60psi I got told I had a flat - twice
I have just about had it with this bike, not spending another dime (read: OK, maybe I'll spring for tires but they deffo won't be Compass) on it.