jack the fropnt of the car up and take off the engine under cover. on the driver's side of the engine there should be an oil filter( you might need to take one more cover off) the oil drain bolt is on the oil pan. i believe its a 17mm
the lock button is to overide so you can change gear with out the key in the ignition or the brake depressed. its convinient when you need to move your car quickly when the battery is unplugged or something.
the wheel bearings may have some to do with but after 10 years no matter how many or little miles it has on it the weight of the engine and trans is on the engine and trans mounts (but i guess if there are very few miles on it its less of a problem) i recently changed both my motor mounts and trans mounts with some other things and a world of difference i felt. its more or less a new car! no vibration no noise of engine floating on a cloud feeling again
it helps if you have a ramp but well get the front of the car high enough so that you can crawl under it then jack up the trans a bit to take the load off of the mount. there should be a brace between the trans take the 4 bolts off then the brace comes off oh and the 4nuts? that are attatched to that is the mount to the brace( i know this sounds confusing) then it should just be another 4 bolts to take the mount off. good luck oh use a small piece of wood between the jack and the trans.
try check your sun roof it starts to sink after the years and then the rubber linning starts to make noise with the wind. the sun roof can be shimmed to raise the height.
all you need is a half inch drive off of a breaker bar to "un" tension the tentioner. then slip it off. you might need to take the fan off. the belt diagram should be on the inside of the hood or somewhere in the frontal engine compartment.
common problem just check coolant level( like you did) and its ok so the sensor is a bit dirty or worn or what ever it is everybody has the problem. you cand try and clean it or buy a new one