I have a 5 speed 2004 mazda 6 - when i accelerate and shift gears the engine makes a loud noise - i have taken it to be looked at and no one has been able to find where the noise is coming from. What can cause this noise?

Based on the symptoms you have described, it sounds like there may be an issue with the transmission in your Mazda 3. The loud clicking sound when shifting into reverse could be a sign of worn or damaged gears, while the hesitation and lurching in first gear could be due to a slipping or malfunctioning clutch.
It's also possible that there could be an issue with the transmission fluid, such as low or dirty fluid, which can cause shifting problems and other issues. I would recommend having a qualified mechanic inspect your vehicle to diagnose the exact cause of the problem and recommend the appropriate repairs.

A loud whining noise on acceleration in a 2010 Mazda Tribute could be a sign of a few different issues. Here are some potential causes:

1. Power steering pump: A whining noise can be an indication of a failing power steering pump. The noise may increase when the steering wheel is turned.
2. Alternator: If the whining noise increases with engine speed, the alternator may be failing. This is because the alternator is responsible for charging the battery and powering the car's electrical system.
3. Transmission: A whining noise during acceleration could also be a sign of transmission issues, such as low transmission fluid levels, worn bearings, or a damaged gear.
4. Differential: A whining noise that increases with speed could also be a sign of a failing differential. This is the part of the car that transfers power from the engine to the wheels.

It's important to have a professional mechanic diagnose and fix the issue to prevent further damage to your vehicle.

The engine may misfire and/or buck while driving at freeway speeds with no fault code stored in the powertrain control module (PCM). This can be caused by an intermittent fault with the camshaft synchronizer assembly. This condition can be diagnosed by monitoring knock sensor data as per Ford service bulletin #05-22-12. Replacement of the synchronizer assembly will be required to correct this concern.
https://repairpal.com/engine-buckmisfire-at-freeway-speeds-934

I hope this helps

have the fault codes read and use a quality injector cleaner in the fuel
it could be low fuel pressure , injector problems or accelerator position sensor related

My Mazda 6 2006 model jerks and goes off then refuses to start. What could be the cause?

Sounds like a bad cv joint. Easy way to check is to raise the front of the vehicle so both front tires are off the ground. Use jack stands under the vehicle and block the rear tires. Start the engine and put the tranny in drive. Let the front wheels rotate while the engine is idling and turn the steering wheel slowly in both directions. Listen for the clunking noise. You may have to speed the engine up a little to make it work.

clutch.

Could be something jumping around in the exhaust. Is your catalytic conv in that area?

This is normally the first signs of Imminent Failure of the Clutch Pack due to Mileage Fair Wear and Tear. It will not get any better, but the final "Death throws" will be significant, insofar as, when you accelerate in a HIGHER gear, the Engine will start to speed up as the FRICTION PRESSURE between the Clutch Plate and the Flywheel decreases. The same as when you drive an Auto shift, the engine over speeds until such time as the internal mechanism shifts up a gear.
Hope this helps you work out a plan.
Regards,DT

one thing to check is rear engine mounting i have had a stone wedged in one and it causes a nasty noise when accelerating