Front End grinding noise- please help!

I just recently purchased a used 2000 GMC Jimmy SLE front end drive and at high speeds on the interstate(anywhere from 60+mph) it shakes a little. Also just recently it started to whenever i have to stop really fast and hit the brakes hard, the front end shakes really bad and makes a grinding noise. Also occassionally, not always, when i am at a stop and start to accelerate after a few seconds it makes a grinding noise. I dont think its the transmission because it doesn't always do it and never slips and i really dont think its the enginer because its only in the initial stages of acceleration if it even happens at all. Any help would be really appreciated!

Immediately pull your wheels. Check for grooved rotors and uneven brake pads. Check your ball joints and your hub bearings. One of those is going out.

thanks a bunch for the help, i guess i will check it out when i get home, any idea how expensive it is to replace bearings or hubs?

The hub/bearing is 1 unit, they are about 120.00 a piece

I got home and took off the tires and the rotors look fine- the drivers side calliper would shake a little when pushed against- prior to taking off the front wheels, while they were still completely bolted on, i grabbed the top and bottom of the wheels and shook the tire. the tire had some give in it and would shake some- both the drivers side and passenger side did this, is this normal? if not what causes it?

Since both sides of the rotor are smooth yet you could shake the wheel, then it's the hub bearings... You need to replace the hub.