PC making grinding noise on startup, need help!

Hello,

This has been happening for awhile now but everyday when I first startup the computer it makes this grinding noise that lasts for about two minutes then it goes away and is fine for the rest of the day when I use it. At first I thought it was dust so I took it out and cleaned it up a bit with a can of compressed air. After trying that, the noise is still there. I don't think it's my hard drive since I use a SSD.
I haven't gotten a chance to open the case and carefully listen where the noise is coming from but one thing I do know is when the noise is happening and I thump the case with my hand a few times it seems like one of the fans inside makes this lower power noise thing and then slowly comes back up to normal. Keep in mind this only happens if I thump or hit the case with my hand. I'm planning on opening the case soon and see what it causing the noise but I'd like an idea if you guys know if what could be causing the noise so I know what to pay attention to. And what can I use so I can hear better where the noise is coming from?