Do you carry your inhaler in your pocket? If so, maybe it is getting slightly compressed as you move and letting the propellant escape?
I agree there is a wide variability in inhalers between brands - I had one where the propellant was too irritating, when I told the pharmacist he found a different one for me. My insurance didn't care as long as it was generic.
Have you looked into the possibility of having your Rx filled by Mayo and mailed to you?