Forgive me for only doing a preliminary search of the forum for about five minutes before posting a new topic. I know the buzzing sound from the fan has been discussed previously, but I couldn't find any of those older threads from years ago. I also apologize for the length of this post.

TL;DR summary: the blower fan is buzzing and something under the engine is screeching on random occasions while accelerating.

Details:

PROBLEM #1: When I have the fan blower at its highest setting (typically with A/C off, but turning A/C on doesn't change the symptom) there is a buzzing or constant clicking sound coming from the fan blower. The severity/volume of this annoyance has changed randomly since the problem started approximately 10-14 days ago.

The vehicle is a little over six years old and has just under 69,000 miles. There have been 3-4 instances over the past six years when a dry brown leaf got caught in the system (typically around this time of year, since that's when dry brown leaves are most prevalent) and worked its way through. Once the small pieces of leaves made their way out of one of the vents, the clicking sound stopped immediately. Typically in the past, this wouldn't take more than a few minutes, maybe an hour or so of driving around with the fan on full blast.

This time is different in that the problem has remained for the past 10 days or maybe about two weeks, and it comes and goes intermittently. Also, it happens at all fan positions (face, feet, windshield), which is different than in the past. It could mean there's a single leaf caught further back in the system (before the point where the position selector directs air to specific vents), but my concern is that the entire system is either clogged and filthy with a lot of crap, and/or the blower motor is showing a sign that it's about to die.

On a six year old vehicle, I can live with it if it's merely an annoyance and doesn't get any worse, but I'm concerned that it's going to get louder or possibly die completely. My understanding is that replacing the fan blower motor is a big job requiring the removal of virtually the entire dashboard, but I hope I'm wrong about that. Even to simply access it for cleaning (if it doesn't have to be replaced) is also tedious and expensive.

Does anyone have any experience with this? I vaguely recall a discussion on this forum years ago in which mice had built a huge elaborate nest inside the air flow system of someone's first generation Rogue because the owner had left it parked in his garage for extended periods of time without driving it and the mice had full access for days or weeks to enter and exit the vehicle.

PROBLEM #2: I've noticed some loud screeching sounds from under the hood on hard acceleration at low speeds. Opening the driver window while shutting off the radio and cabin fan really makes it easy to hear. It doesn't matter if I'm hitting the gas from a standing start or if I'm already traveling 10-20 mph and then hitting the accelerator hard to gain more speed quickly.

I had the serpentine belt replaced a week ago ($143 installed including tax) for the first time since the car was shipped from the factory and that reduced about 80-90% of the screeching, but did not eliminate it entirely. It was not a constant problem even on the old serpentine belt, and it did not happen during every instance of hard acceleration. I first noticed the sound when turning and accelerating at low speed, but then I noticed it happens almost as often with the wheels pointed perfectly straight. Now that I have a new serpentine belt, the noise is even more random and infrequent, making it harder to replicate, but it's still there.

I've driven about 200 miles on the new serpentine belt. I was hoping that giving the belt time to break in would solve the problem entirely, but driving these 200 miles hasn't helped with the remaining screeching, unfortunately. What else could be causing this noise?

Everything else is great. No loss of power, no excess road noise (other than described above), no problems starting, nothing. When the screeching noise is not happening, the engine and CVT sound like they're working properly, including during hard acceleration. They're a bit noisy compared to other vehicles because the engine is underpowered at only 170HP, but they sound great to my ears, based on driving this car for six years and getting to know it well.

Update: The screeching on hard acceleration at low speed is all but gone. I guess the new belt simply needed more time to break in. The clicking in the fan blower is still present, but barely noticeable, even with the windows closed and radio off.

Everything else on the vehicle is working perfectly and after nearly trading it for a 2019 Rav4 Adventure model two weeks ago (so glad I didn't make that bad decision) I love my Rogue more than ever.

For all the bad reviews about the CVT, it seems for everyone whose transmission has failed prematurely, there are two reports of someone who has driven 200,000 miles or more on their Nissan CVT without any issues. Just change the fluid frequently and make sure the level is exactly right, don't accelerate hard for the first five minutes of driving after a cold start, and always use OEM long life coolant, doing a full radiator flush every 60,000 miles. Do all that, and you won't have any problems.