2001 Mitsubishi Galant front end vibrates ALOT when car is

Other Category problem
2001 Mitsubishi Galant 4 cyl Wheel Drive Type unknown Automatic 73,000 miles

BROKE COLLEGE STUDENT AND I STILL DONATED :) . PLEASE HELP?

I have a 2001 Mitsu. Galant that I'm having some problems with. When the car is in drive and it is stopped, the front end shakes and vibrates uncontrollably! When the car is in neutral or in park. This problem goes away. This started about 4 months ago but I only bought the car 6 months ago. So the person I bought it from could have done something to temporarily mask the problem. If that is the case what did they do to make it go away? Because I’m broke and I might want to do that until I can get it fixed
Also, I've notice a high pitched whistling noise lately? I think it happens more often when I have just started the car; however I also notice it sometimes after I've been driving for a while.

Can you please tell me what is causing these two problems. The cheapest way I can fix them. And how much it will cost?

Oh yeah.A couple months ago my check engine light came on due to a failed OXYGEN SENSOR. When I took it to the mechanic to be fixed, I asked him to also fix the shaking and vinrating. He said the the new OXYGEN SENSOR would fix the shaking. It didnt.