Q: I have knocking in my engine. But then as I pick up speed it disappears. What could it be?

It sounds like you may have low oil pressure that may be causing some valve train noise as a result of the oil not properly reaching the top of the motor. This can happen for a number of reasons, but should be looked at very soon as it may eventually result in damaged engine components. As you pick up speed the engine rpms increase which cause more oil to be pumped to the top of the motor resulting in the noise going away due to the valve train components receiving more oil.

Generally, however when this happens the low oil pressure light will come on. The oil pressure light will usually come on when a few things could be happening. Either the motor is in fact low on oil, the oil pump could be failing or not pumping oil sufficiently or the oil pressure sending unit is not working properly and may be producing a faulty reading. If the engine is in fact low on oil, you may notice the temperature gauge reading above normal temperatures as a result of the lack of sufficient oil in the motor. I would recommend checking the actual oil level in the motor by using the dipstick. Be sure the oil level reaches the "full" mark. If this registers as "full" then you likely have a faulty oil pressure sending unit. I would recommend having an expert from YourMechanic come to your location to take a look at your vehicle to determine what may be causing your low oil pressure to cause this.