I have a 2005 Toyota Highlander. A week ago Friday, on March 2, I got 4 new tires installed, had the oil and filter changed, and had the fluids and belts checked. Just yesterday (Sunday) I noticed a knocking noise which I think is coming from under the hood but not sure. When the engine is running, I don't hear the knocking when the car is stopped or when I accelerate. But when the car is moving and I take my foot off the gas pedal, I hear the knocking very distinctly. What are some possibilities that could be causing the knocking? Could the mechanics have done something to cause it?
There's no way of knowing without knowing for sure where the sound is originating. It could be loose front or rear suspension components, a loose transmission or motor mount, a bad U-joint on the driveshaft, worn shock/strut, engine problem, driven accessory (ps pump/alternator/etc) problem, etc.