Noise at 2,000-3,000 rpm when heated up
 

Alright so first off i have a 1996 Mazda 626. When the car is heated up to normal temp (between the cold and hot meter gauge), it makes this noise between 2,000-3,000 rpm... Its really hard to describe, and i wish i could describe it better, but the best explanations would be that it "marbles upon acceleration" (thats how my friend describes it).. But does anyone have any ideas on how to fix it???

Thank you for any advice!

First off, you need to find wher it is coming from. Is it the engine, or the heating and cooling system? can you hear it only when driving , inside, outside? Use a mechanic's stethoscope ($5 or so) to track down noises.

I have minivan that makes some "marbles in a plastic cup" noise. I only hear it inside and it comes out of a vent. I believe it is a baffle.

If it's the engine, it might be a floating lifter (because it's loose or gummed up). I suggest that you go to your local auto parts store like NAPA and buy a can of SeaFoam (expensive but great stuff). Right before you take the car out to run errands or before you drive to work pour the entire can in the crank (where you put the oil in when changing the oil) and run the car like normal on your trip. It cleans all the carbon deposits internally and might solve your problem. If it doesn't at least it will make your car run better anyway. I'm just trying to give you a possible cheap fix. I hope it's nothing big. Could be your head needs rebuilding, but I'd try SeaFoam first. What's it going to hurt?

When was the last time you had your valves adjusted? It needs to be done every once in a while even with your DOHC set-up.

Also, what oil are you running? I think you're supposed to run 10W-30 but that depends on where you are. This will make only a teeny bit of difference, but my money is on SeaFoam. I usually do a half can of SeaFoam right before I change the oil and filter.

Good luck.