Just put in optima yellow tops in my hdj81 to replace the origonal jap batteries. did a quick AVR test to be sure alt was working properly and all ok. However when i got home today i poped the hood to check up on an old oil leak i recently fixed i could ever so lightly hear noise coming from the batteries..... further inspection lead me to the small vents they have on their tops, thats where the faint noise was coming from. I have never owned optima batteries before and was wondering if this is normal or are these bats f'ed??? the last thing i need is a battery to explode under the hood!