Update your post to include full system hardware specs and OS information.
What are you doing when the noise/fan slowdown occur? Gaming, light work, browsing online?
Any new hardware, software, software, or OS updates about 2 weeks ago?
Look in Reliability History for any events that correspond with the noise and fan slowdowns. Any entries that started appearing about 2 weeks ago.
PSU: Corsair CV 650W
Whenever it makes this noise the fan slows down then it goes back to its original speed. Been going on for about 2 weeks now. Only had the PSU for 2 months .