Have a 2009 elantra touring manual transmission. it makes low noise from the transmission, when in neutral. as soon as i hit the clutch the noise disapears.what could it be? thanks

You need to locate the source of noise first , it seems to noise of drive line only. Which consist of flywheel , clutch system and gear box.
1) In case you are having same problem with clutch engaged or disengaged position ( while throttle is on) , then there is a possible problem with the neutral gear ( if it is not abnormal but just high in magnitude than it was previously than consider replacing the transmission oil) otherwise get the gear box checked with a transmission specialist.
2) In case you are having the noise problem only when clutch is engaged than u may consider to refit the clutch plate and pressure plate , there could be a problem of torquing.

There are a couple of things to check. If your power steering pump is low on fluid, or a bad bearing is in the Alternator, they will whine. The PCV valve or any hole in the Vacuum lines will whine as RPM is increased. Even having the Air filter box not fully seated will make a whining noise.

Now both automatic and manual transmissions can whine as RPM is increased. Check fluid for each.

Serpetine belt and pulleys-can make noise.

Sometimes you can shift into neutral at any speed and the engine rpm will drop almost instantly as the car rolls at speed. If the problem disappears as soon as the rpm drops, then an engine part probably is the reason.

Might be your transmission. The throw-out bearing is stationary when the clutch is not engaged.

This is noise caused by gear roll over, in modern manual transmissions a very thin lube is used, in most it is just regular ATF not the must thicker gear oil so this roll over noise is made worse. This noise is to some irritating others don't seem to notice. This noise doesn't affect operation of the manual transmission at all and even if you replaced all the bearings and gears in the transmission it would soon return as things wear in and loosen up. If you switch to a light gear oil it will make the gear roll over noise quite down but the transmission will be hard to shift cold.

I would be checking the throwout bearing. But, if the clutch isn't slipping, maybe leave it for now?

If you put it in 5th gear, let out the clutch with handbrake applied and it stalls--the clutch isn't slipping for sure.

There is two possibilities, 1: the vehicle has more than 90.000 and needs a clutch and the other the hydraulic system is leaking, to inspect open the hood and find the little reservoir make sure not to inspect the brake fluid level, if the fluid level is low look for the source of that leak, start at the most common place the clutch sleeve cylinder attached to the manual transmission, then the line from the cylinder to the reservoir, if all this is dry, my friend you need a clutch.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/flavio_517b938f50183b92

well if he tighten the wheel hub bearing nutt to tight it will cause the hub bearings to burn out.....But he is a tec write, So im sure he did it right. Also the noise from the rear mabe something you are heareing now because no noise in the front is gone and the back noise is heard at this point......
good luck to ya.

Don't do it. If you tow a Hyundai on all 4 wheels, like behind an RV, the transmission will burn itself up! The manual trans requires splash lubrication for the bearing and gears, which it doesn't get because the transmission has to be in neutral. The automatic transmission burns up the one-way clutches.

Your clutch is bad it and the pressure plate will need to be replaced and the flywheel will have to be surfaced, yo will need to replace the throwout bearg as well.

SOUND LIKE TRANSMISSION IS SLIPPING.CHECK THE TRANSMISSION FLUID MAKE SURE ITS NOT LOW.ALSO IF TRANSMISSION FLUID LOOKS DIRTY DARK AND SMELLS BAD REPLACE FLUID AND FILTER.IF FLUID IS GOOD YOU HAVE.TRANSMISSION OIL PUMP AND FORWARD CLUTCH PROBLEMS.