Whining noise i have a 99' toyota tacoma and i installed new headers on it today. upon startup i noticed it idles roughly and makes a whining sound through all rpm's. what could the problem be?

Any codes?

Is the check engine light on? If so what codes are present? What engine is this?

Open the hood. Listen for where the noise is coming from. Fix the thing that is making the noise.

remove the belt and start the engine ..IF THE NOISE disappear it might be idler bearings that driven by belt but if the noise still there check the pcv valve..

I never suggest flushing a trans

Just remove the pan & clean

If you want most of the fluid out,
drive it a week or so then drain again.

I suspect the noise is the trans pump,
but don't know exactly how any dirt sediment
flushed into it would cause a noise

ther is probly leaves or some trash in the blowermotor you will need to remove it lower righthand side of dash just 3 or 4 bolts the clean it out

Check your belt. Belts will whine when they're worn, cracked or glazed. I hope this was helpful. It's not normal. Take care and God bless.

Bryon

Possible fuel delivery problem, fuel pump, fuel line, clogged fuel filter, leaking injectors or injector O-rings, faulty pressure regulator etc. Check your fuel pressure.

I don't know how loud the noise is, but its weird that you mention 50 mph. At that speed or above you are keep a constant rpm level. I say this because it might just be your air box loose and the sound of the intake air is making it. A 2008 truck should not have any major problem. Sometimes an alternator will sing or whine but never heard anyone say something is whistling. One other thing is sometimes for some reason ive heard a noise like that coming from the speakers of my car that goes up and down with the speed of the motor, but that was when I was tinkering with speakers and sub outs and amps. Thats all I can think of.