Steering "locking up" when going at high speeds on 2004 Mercury 4hp 4-stroke outboard motor?

I have a 2004 Mercury 4 horsepower 4-stroke motor. The motor seems to run fine, but there are 2 things that have caught my attention:

1) Whenever I switch the motor from Neutral into Forward, the motor seems to jump a bit and makes a loud thud. I'm not too worried about this, since me and my dad assume it's normal.

2) This is more concerning. Whenever I switch the throttle to any somewhat high speed, the steering suddenly "locks up". When this happens, I can only easily turn it to one side, and it will only turn slightly to the other. So I'll be able to turn it right with no problem, but then it won't go left. If I force it, which takes a lot of effort, then I can make it "switch sides", so I'll be able to turn it left with no problem, but then it won't go right.

Sometimes, it even locks up so that I can barely steer it in either direction, though this has only happened occasionally. This has also happened slightly once or twice while driving slowly, though it's not nearly as hard to "switch sides". It almost always steers fine in all directions at slower speeds, but at higher speeds, it just locks up.

Does anyone know if the first one issue I mentioned is normal, and whether or not it is even a problem? And could anyone help me figure out what may be causing the second one, and how I can fix it (or if I'll need to take it to a mechanic)? Thanks!