well brothers, as for the first question car vibrating when at a signal , is it when you press the brakes or when you start moving or when you are driving normally at a specific speed, please indicate your vibrating or tell me the whole situation, i.e the time when you experience this vibration and the way your car vibrates ( cause there can be different types of vibration ),
now the second question which is from Mr grey, wheel balancing can go out of order due to various things,hit a speed bump real hard, hard enough to damage your wheels, try to park on a pavement a foot path, drive a bit fast on a bad terrain like off road, drive on those reflective markers on the side of the road not the small ones im talking about the big ones that make your car steering wobble, drive your car on broken road carelessly like in sharjah or any remote area and etc etc their are many many reasons or actions that can damage your wheels. now even if you drive very very carefully balancing going out of order is very much possible with out any of the above mentioned issues, how? let me show you.
look at your wheels carefully if its a steel rim you have to remove your wheel cover if its an alloy rim you dont need to remove any thing only in case of a really expensive rim you need to look it up from the back side i mean the inner side, you will find a small piece of metal stuck on the edge of that rim it will be rectangle, a small piece of metal, that is the thing which is balancing your wheel's weight, some time they fall off because they are not stuck permanently they are just latched to the edge of the rim so when they get old or you rub wheels with a pavement while parking your car, they get ripped off, that way your cars wheel loses weight balance and that specific wheel starts vibrating which make your steering wheel and your car vibrate like hell.