Q: Engine makes clicking sounds while idling and at lower speeds

Hey there. The first noise you described sounds like valve lifter noise. You will hear this sound if the engine is low on oil. Check the oil level and add if necessary. The lifter noise is not heard at higher RPMs because the oil pressure is higher as the engine speed gets higher. If you have high mileage, you could benefit from the next higher viscosity oil. For example: a car that originally called for 5w30 when the mileage gets up past 100K, you can use 10w30. The reason is because as bearings wear out it becomes harder to maintain oil pressure and a slightly thicker oil can help get some of that oil pressure back. I’m not sure what noise you could be describing, but there should not be rocks in any engine pipes. It is possible you have a cracked exhaust pipe or something else loose that is rattling against a pipe. A certified technician from YourMechanic can come to your car’s location to inspect the car noise and make the correct repairs.