Thank you Casper for your advice. I did it yesterday, remove the filter by carefully bending (and saying really bad words to the Japanese car designer, who put the cabin filter to that tight spot). I closed all the diffuser on the dashboard to prevent debris (and pollen) filling inside the car and cranked the fan. A lot of dried leaves come out, that is amazing. In just 4-5 months (summer) that much stuff accumulated inside the fan! After that I put the filter back and run the fan. There was still the same noise, but this morning it is all gone. I am pretty sure the stem of a leaf or pine needle (whatever it is) is rotten or dried and broken by the fan blades.
However now I have another concern. After I run the fan without the filter, I realized that the AC radiator is just 5-6 inches away from the fan and all the debris and everything is thrown directly to the radiator. I am sure nothing was there sharp/hard enough to cause a leak, but I hopefully did not block the radiators fins!
I think that is a design problem. See Phillip has a 2010 Rogue and he (I guess) passed a Fall season with his car, which is maybe the reason of the problem. Maybe he parked his car under a huge pine tree etc. But I bought the car on Feb. 2011 and there were just snow on the ground. No leaves. If in just 4 months the fan is full of that much stuff, I cant imagine what will happen after 3-4 years.
By the way, I opened the hood and cleaned the intake grill at least every week.
And Phillip, I have an idea. Close the vent outlets on your dashboard, remove the cabin filter and blow air (maybe use the pressurized air at a mech. shop) from the filter opening. This way all the stuff will follow the air intake grill and blown from the intake grill (the air will pass through the fan blades, cause it turn.Hoping it wont damage the fan). Don't forget to open the hood though. Just give it a try.
