I couldn't tell exactly, it wasn't high pitch one, but was loud cranking type of noise as if either something was in a way of fans which wasn't the case, or transformer/capacitor was going to blow up but not too electric discharge sounding. I expected noise to continue when I turned it up again, but it runs normally now like it did before. No insect can get in there, and I don't have many of those in my house except occasional fly get inside of house with back door opening.
Now that I think about sometimes I hear very very quiet high pitch sound but I was thinking it was one of the fans
High pitched screeching-like sounds are usually capacitors attempting to commit suicide. I'm not sure how well you can look inside your PSU, but if you see the capacitors bulging at the top, then they're getting close to giving out.