It could be several things, your bearings could be under a pre load, which means there is exesive pressure on them caused by them being over tightend, it could also be as simple as a brake hanging up on the drum or disk. you may have a bent rim possibly but that would cause the car to vibrate. Also you may have a worn spindal, the shaft that the bearings slide onto. You could possibly have a brearing catching or binding up. I would definitely have it looked at so you don't have a bearing go out because it could mean you lose you tire completely.
needs new wheel bearings
check wheel bearings and cv joints if applicable
First, check the lug nuts. If that's not it, check the wheel bearings.
Assuming this is an older car a knocking noise on turning could mean one of the drive shafts is worn. Other things to check - are the bolts tight on the front wheels, if a very high mileage it could be worn wheel bearings.
If you grab it in the 12 and 6 o'clock positions, you are typically checking for play in wheel bearings and ball joints. If you grab it in the 9 and 3 o'clock positions you are typically checking for tie rod ends or wheel bearings. But you are not totally limited to these although the most common.
Power Steering?
No, bad front wheel bearings would not prevent a transmission from shifting. If your car has bad front wheel bearings you will notice wheel noise or wheel looseness.
Yes they can make a grinding noise, if they are bad.
Wheel bearings or u joints
Check your wheel bearings. Mine made a noise when turning right and had to replace the wheel bearings and hubs as they are all one unit on my 92.
I experienced a knocking noise in my 03 Xterra and found out is was a bad wheel bearing seal and had to have the Nissan dealership replace it for about $400 (includes labor and parts).
A grinding noise usually indicated bad wheel bearings.