The last couple of times I've checked my air pressure in my tires I've had to let some air out. The pressure is higher in some tires than it had been previously. I check roughly the same time of day, the vehicle has been sitting in a garage out of direct sunlight and has not been driven prior to checking. I can't figure out why the pressure in 2 of the tires is going up each time. I think it is the same 2 tires each time also.