Vibrating Subaru

[fourcars]

I have had my car to 3 specialty shops for a vibration that occurs only when in gear but standing still, like at a red light. It is getting more pronounced and gas mileage is diminishing. It began quite suddenly after having the front left axle and boot replaced. Everything has been checked and I am told “don’t know what it is but it’s harmless. Go ahead and drive it.”