Weird humming noise that comes only when the engine is hot
 

I noticed that my Maxima makes a weird humming noise when the engine gets hot. It started making this noise only since a few days ago. I typically drive the car 15 miles everyday. Of late she started making the humming noise when the engine gets very hot (like after driving 10 miles). That makes me think it may have been something to do with the engine coolant. I did check the coolant reservoir and found it was empty. Filled it with coolant (a pre-diluted mix) some two days ago. However, even now, the humming noise persists. I noticed that the noise only comes when the engine is very hot and I have taken my foot off the gas pedal. If I press the gas pedal even slightly, the humming noise stops.

I have a video that describes the noise ( https://drive.google.com/file/d/1tzX...ew?usp=sharing ) . It seems to originate from the passenger side firewall.
I had never turned the AC on, so I doubt it comes from the AC.


Any hints/ideas what may be happening ?

Thanks for reading.

The timing chain tensioner guides are up for replacement IMO.

Thanks for reply. I am curious to understand why the noise only comes after driving the car for more than 8/10 miles. I understand that changing the timing chain tensioner guides is a "big" job and definitely not DIY (right ?), is there something else that I need to rule out before ?

It can be DIY and even w/o dropping the subframe from what I understand. The engine top oil pan, intake, valve covers and VTM have to come off to gain access to the tensioners.
I have a Quest with the same engine which has just been ruined during the timing chain job by an incompetent shop which claimed that they knew what they were doing. Their mechanic shorted something somewhere and blew the ECU and probably some sensors. I lost the otherwise perfect 2005 Quest with only 110k miles on it for several months and counting.
You might be much better off DIY.

Thanks for the reply Tarzan. I have gathered some more data points that I would l like to validate with you.

1. One interesting observation I noted was the humming sound, only came only when the car came to a stop at an intersection after running more than 10 miles.

2. During such times, if I very gradually increased the engine RPM from 1100 to 5000 rpm, the pitch of the humming noise did NOT change.3. Till a few weeks ago, I was required to travel some 15 miles (one-way) from home to office or back but over the last two weeks its reduced to around 6 miles one-way.
4. Over the last two weeks, I have never heard the humming sound ever (when the car travels less than 6 miles at one go).

Everything is possible. You never said how many miles on your Max.
Today I went and looked at a 2013 Quest for sale. It has the same engine as your Max and my old Quest. It had about 80k miles and I could hear the telltale sound of worn chain tensioners which did not seem to change with RPMs. Now that you mentioned that I did realize, that on my Quest the sound also did not change with RPMs. I do not know where else it might be coming from or why only after some driving.

Many thanks for the reply Tarzan. My Maxima has done well over 160K miles. So yes, the chain tensioners could definitely be worn. Thanks for taking the time to reply to my questions.