How many miles? They can wear out, there's no harm in changing the tensioner. Might as well change the belt too, they aren't too expensive.

 

Well after replacing the tensioner the noise was still there I narrowed it down to being the alternator pulley which by the way you can't just change the pulley it's a whole assembly (great design if you want to charge the hell out of your customer) $333.33 later with a $75 core return she runs like new. Not too bad compared to the $590 + tax Nissan quated me for parts and labor! They were really surprised my alternator was bad I guess it's a pretty rare thing for one to go on an X. Anyway this is just a heads up incase someone else runs into a funk knocking noise around your belt.
Posted via Mobile Device

 

You could have gotten an alternator much cheaper elsewhere.

 

Glad it got taken care of, good thing to invest in is a mechanics stethoscope. Might help narrow down the noise next time

 

I have a very similar knock on the front of the engine, to me it sounds like lower drivers side. I have a new belt and plan on seeing if the bearings are shot on any of the pulleys. I have my fingers crossed that it is the tensioner but I am realistically thinking it is probably my alternator as well.

 

when mine started it didnt know where it was coming from at all that engine bay tends to send a nice echo! even when i took it to the techs down at nissan they were like dude wtf ive never heard anything like that... i could see the tensionor jumping so just backtracked the belt and i actually have to crawl underneath to get a really good view of the alternator pully close enough to where i could barely see it bounce around and when it did it was causing the noise so took the gamble hoping that it was the originating point of the noise. and yes a thesascope is a good investment just never needed one, but a long screwdriver will work just as well if you put the head on the component and the handle to your ear you should be able to hear if the bearings are going out. ive never personally have done this haha but ive heard of it being done obviously be careful where you put it you deff dont want the screwdriver or your hand getting cought in any moving parts that would make for a bad day!! i heard a horror story today from a guy at work his pully was going out and it got bad enough to where the extra tension on the belt caused by the pully bouncing actually put enough strain on his water pump to ruin it as well, so not only was he out an alternator, and a belt but a new pump as well. good luck id recamend tackling it asap.

 

I only have one vehicle so even though I did shop around and pricematched this was on a saterday and I think the only place in Utah that had one in stock was 45 min away they got it to the parts store a day early actually so I know it may have been a bit upped in price but being I had to work Monday and needed a vehicle I guess it's not too bad. I got very lucky cus the next soonest time one would be in was Wednesday...
Posted via Mobile Device

 

almost forgot when i took it to nissan they prettymuch narrowed it to the alternator or the compressor for the ac i think the comp is on the drivers side so that very well could be why you hear it from the drivers side.

 

Amazon...hitachi reman. It was $165 shipped next day with amazon prime.

 

sounds like a sweet deal.

 

mine has a very similar noise to what your describing, looks like i'll be taking off the belt and see if I can narrow it down to which pulley may be bad.

 

afetr you take your belt off, reinstall your airduct and vacuum hose and crank your x up (dont let it run too long, just longenough to inspect the pulleys) see if you still hear the noise, this will help narrow it down to see if its actually any of the pulleys on the system. no noise = a component/pulley within the system is causing the knocking. if you do hear it still then you have bigger problems within the engine.