Frigidaire refrigerator model number FRT21LRG, about 5 years old

Freezer on top

The fridge started making an occasional humming noise about a week ago.
At first I thought it was just something vibrating, but then it started
to do it more often. On Monday it started to do it quite a bit, and I
noticed the freezer was thawing out. Pulled the fridge out from the
wall and noticed the humming sound was coming from the compressor. It
will hum for about 5-10 seconds, and then it's quite for about a
minute...then hums again for 5-10 seconds... Unplugged the fridge for
an hour, and plugged it back in. All was fine for the next 12 hours or
so, then it started to make an occasional humming sound again. Now I am
having to unplug the fridge every 6 hours or so. Father in law says
it's the defrost timer...I think the compressor is going bad. If it's
the defrost timer...wouldn't it be stuck in defrost mode or non defrost
mode..i.e. the compressor would either be on or off the whole time.
I think the defrost timer is turning the compressor off every six
hours, like it should, and then the compressor is not able to come back
on like it should. Only after cooling down for an hour is the
compressor able to come back on.

Any ideas?