I have a very loud sound coming from under the hood, almost like a belt or something is loose. I just had a tune-up, but the Check Engine light is coming on. When shifting gears, the indicator doesn't match what the car is actually doing. I recently got the transmission replaced and a tune-up. The Check Engine light still comes on and now the truck is making an extremely loud noise under the hood.
I'm guessing when you say that the "indicator doesn't match what the gears are doing" that you mean the RPMs go up but the vehicle doesn't accelerate. This is an indication that the transmission is slipping. If you just have the transmission replaced, I would take the vehicle back to whoever did the job so they can make it right. As for the noise under the hood, these engines are known for blowing the spark plugs out of the cylinder heads. This will make a very loud noise and also turn on the Check Engine Light. However, I wouldn't be able to tell if this is the problem with your vehicle without inspecting it first hand. There are countless other reasons for engine noise as well. I suggest you have a qualified mechanic, such as one from YourMechanic, diagnose and repair your engine's noise.
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