Hissing brake pedal ?

Hello all, I have just read all 28 pages on the" brake please read this" topic =thread, we have only had our p38 about a month and just the last 2to3 days I have noticed a slight hissing as I apply the brakes ? is this normal ? the brakes work fine now and then it takes the lights a few seconds to go out after start up the abs light always goes out once speed is over 5 mile per hour as stated in the manual ,I am not getting any clicking sound at all as this seems to be the main problem in the "brake topic". any advice or thoughts graciously received thanks ps ours is a late 1996 4.6 hse running on sequential lpg system and one of the most comprehensive service historys I`ve ever seen with thousands spent and 117.000 miles on.