Clicking Noise 1Z Engine: Fuel Injectors?

I have another question (please excuse the many questions, but I just want the engine to last a long time). Lately, I've been hearing a metallic clicking sound, accompanied by a knocking noise, more and more often when the engine is idling. It doesn't happen very often, but it's happening more and more. Could it be that the injectors are failing, or are they just slightly misaligned? The machine now has about 160,000 km (approximately 99,000 miles) on it and is actually running well, but the knocking sound combined with the clicking is a bit concerning.

Best regards, WarLord.