Hello. My car has a mileage of around 4,000 and a manual transmission. The issue happens when I drive around 30 miles. The transmission fluid gets hot and the car start having this weird gear lash sound. It can be heard if I accelerate around 2500 RPM, no matter what the gear the car is in. Why is this happening? Is this a serious issue? Thanks.
The noise may not be coming from the transmission but the engine since you say it happens at 2500 RPMs no matter what gear is selected. You may be hearing the intake manifold runner control noise changing at that engine speed. It may be a normal noise or it may require an intake manifold replacement on some of these if the noise is bad enough. I recommend having a mechanic inspect the noise in person to see if it needs repairs.