All of the sudden, with only 40k on my truck, the blower motor decided to become incredibly loud in my truck. Sounds like a strong vibrating type of noise on high speed. Almost as if something were caught in a fan... Is it going bad already? It still blows, it's just loud.
Have you checked if part of the filter has come loose? It sits right on top of the fan and if the paper has torn it would get sucked right down into it. On a different track, is it a OE blower motor? Bought my 06 used and it had a VERY noisy fan. Checked everything. Finally found a OE one at the junk yard and now you can hardly tell its running.
The first course of action would be to remove the cabin air filters and inspect them and you may be able to get a look inside the blower fan, as well. You may need a dental mirror and a flashlight.
I had to replace my blower in my Xterra. I bought one online for about $80, it was about 10X louder then stock. So, I'd recommend buying OEM if it needs to be replaced. Takes about 15 minutes to change.