i drive an automatic toyota premio car and it makes a straining noise as it picks up speed and but normalizes when i slow down. What could be causing this?
A straining noise that gets consistently louder in pitch and/or volume as the car gets faster is usually a sign of a worn bearing in a wheel or it could be a problem in the differential (rear wheel drive) or transaxle (front wheel drive). As the car moves faster the wheels and the mechanisms that drive the wheels spin faster making the bearings move faster, and the bad bearing makes a louder or higher pitches noise.
It could also be a piece of road junk that has gotten wedged in a wheel well or a piece of material from the car itself that is rubbing, as the wheels move faster there's more rubbing and more noise.
If the car is pulling one way or the other you could have a stuck brake on the side it is pulling to, it's also possible you have a stuck emergency brake. Those are less likely scenarios.
Where the noise is coming from will give you the best clue, wherever the noise is is where the problem is. If it seems to be coming from a particular wheel then that's what needs to be checked. If it seems to be coming from the middle-front of the car then it's probably in the transaxle or CV joint.