I study while listening to the radio and I have a pretty old one on my desk (it still has a casette recorder). It has a big steel antenna that can be stretched. I usually has some noise because it's pretty hard to get exactly the right frequency, but when I touch the antenna it sounds clear without any noise.

I just wondered why it does this... Last year we had the same thing with our radio on a scouting trip on an island and we had a portable radio with us.

I would also like to ask why my radio goes from good to just HSSSSSSSSSHHHHHHH just because I move further away from it, if you don't mind.

Like you it's been bothering me.

you are an antenna

Exactly. Sometimes just standing in a right spot can make a radio signal better. Or worse.

The human body acts as an antenna.
You could try clipping an extension antenna on (for FM, any non-galvanized metal wire attached to a alligator clip works well). Or if your radio supports an external antenna, then go out and get a powered tv antenna, which will also work for FM.
Weather can also affect reception, flourescent lighting, proximity to high powered circuits, large buildings in the area, etc.