Hey scotty,
A little over a month ago, my Nissan Xterra started to make some weird howling noises from the engine bay. The car has a little over 200,000 miles on it and has no significant issues other then this noise. It is a 2005 4.0 litter, Nissan Xterra SE, with automatic transmission, with activatable 4 wheel drive (pretty decent off-roader). Bought it a little over a year ago and been pretty satisfied with it.
https://www.youtube.com/watch?v=0r8o2wOE3HI
This is a link to the video that I uploaded on youtube, to show how it sounds. I compiled 3 separate videos I took of the said howling noise, since those times are the only times I could capture it while the car was not driving (the noise came up ONLY these 3 times when car was idling). You can even notice that the sound it makes is not consistent and changes.
The conditions in which this sound comes up is VERY inconsistent. I might even drive for 2 whole days and the noise might never even come up. The only condition that is consistent is that, if I floor it and then let off the throttle, while the RPMs drop the noise starts to come up. Then, it might even go away and never come up again. If it stays, it goes away as soon as RPMs reach 2000 and over. Basically, the noise disappears on high RPMs like it never even happened.
The noise is heard during low RPMs, although, past 4 days it is only heard when I keep the RPMs dead centered on 1000, no more, no less. Giving it gas has no impact on the noise's pitch. The pitch doesn't change whether the RPMs are high or low. It sometimes changes randomly and doesn't care on what RPMs the engine is on. It might change the pitch even if I keep the RPMs constant. This occurred only twice.
The car has no problems with driving, or idling. Nothing and I mean NOTHING has changed in the car's driving capabilities. It is all fine, only with the noise added. I thought it was the belt which I changed 2 weeks ago since it is a quick and easy fix, but didn't help. If it is timing chain related I am planning to change that in couple of weeks, when my trusty mechanic comes back from his vacation. It even might be one of the belt pulleys. I honestly have no idea what could it be, coming from the noise's inconsistent nature. I have never encountered such a situation. All my previous cars would make constant noise, when something was off, or broken, but this?... This is really new to me.
If anyone can help me understand what does this howling noise mean, would be greatly appreciated, since unfortunately I don't have a lot of time and resources to troubleshoot, through trial and error. This car is my daily driver and only car that I own at the moment and I don't have the luxury to park it in a repair shop for days.
Thank you in advance, for your time.
All right, when it's Halloween, get yourself one of those electronic stethoscopes and start listening to everything closely. It could be a bearing a starting to go out and either water pump alternator and it will kind of howl like that. The only other Halloween I've seen like that was internal to the intake manifold where either a PCV valve was vibrating and hooting like that or there was some kind of restriction inside the intake where air rushed over and made that noise
I changed the water pump, so it is brand new. Haven't thought about the PCV valve, because is sure feels like the noise is coming from behind the engine. And surely enough the PCV valve is located behind the engine. Guess I'll have to take off the intake over the next weekend and see. if that's not the case, then it will be a bearing going out.
Thank you very much for the answer.