My car had the exact same issue about a year ago. I can not at all tell you that this is how to fix your car but I can tell you what I did and it resoved it. The confusing part that happens alot is there's alot of times when you are trying to correct something or make a repair and you end up touching/adjusting a half dozen things and it's fixed. But your not sure if it was one of those things you did or the whole combination of items that you touched. Know what I mean??
-Here is what I did: My choice of engine oil is and always has been Mobil1 Extended Service 5W-30 along with 6 0z. of MILITEC1. I use Amsoil Ea oil filters (K&N or Mobil1-Second choice). I installed a Screamin' Demon ignition coil with Autolite copper core plugs gaped at .054. Installed a set of Granatelli MPG plug wires (green ones). Replaced the pcv valve. Cleaned the MAF sensor with cleaner labeled for MAF sensors. Lastly, most importantly, I Seafoamed the upper intake manifold through the pcv valve and added one full can to the gas tank. Problem was solved and has never once ever shown its face again at all.
-I think I know how you fill. I Can Not Stand ANY Noises, Ticks, Squeaks, Of Any Kind! Drives me nuts!! Good luck with it. Please update when it's running perfect again. At the very least, I recommend you put on a high quality oil filter to insure no oil drain back from the engine.
-FYI: American Muscle now sells Amsoil oil filters at a great price. They are garaunteed in writing for 15,000-25,000 mile interchange. I use them for 7500 miles but not matter what they are great quality.
