Hello i have a 99 Nissan Maxima se 5spd manual, when i get up to 65mph to 70mph ill here a buzzing type of sound coming from the engine bay. if i back off the gas and drop below 70mph it goes away, if i continue and go to like 80mph and above the sound goes away completely but when i let it slow back down right when it passes through 60-70 range it comes back then goes away for a split second. somedays the sound wont even be there at all then it comes back next time i drive it. the car doesn't seem to be running any different, also its been doing this since like 165000 now it has 180000 but the sound has altered a little bit. please help i really need to solve this.

 

You may have one of the metal heat shields coming loose. Check the exhaust manifolds and exhaust system that everything is tight.

Sounds are tough to diagnose over the internet.

 

If its Buzzing through the speakers is alternator whine, and in this case means your alternator could go bad. Redo your grounds for starters if that is where its coming from.

From the Engine bay? Your sure?

 

yes almost positive, its like a buzzing/tapping/woodpeaking sound kinda but it will make the sound if im in gear or if im in neutral, whenever i get to the 65-75 mph range, i never hear it below or above that. but sometimes it doesnt do it at all, like yesterday i didnt hear it at all but today i did. its mind blowing to me.