I have a 1.5 year old Optima Red Top (34R) in my 4Runner and noticed a hissing sound coming from it after driving it yesterday. The 4Runner had been sitting in airport long-term parking for 5-days. I drove it home yesterday and when I parked it noticed a hissing sound coming from the engine bay. After checking it appeared to be coming from the vent nearest the Positive terminal. Is there something I should be concerned about or is this normal and I have just never noticed it before? Thanks.