clicking sound in engine on 1997 Volvo 960

There's a clicking sound in my engine that speeds up when I'm accelerating. My volvo sounds like an old Mercedes diesel. What is the problem?

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1 answer 1 comment
This may be an exhaust leak, or a noisy lifter. Is it noisier in the morning when the engine is cold? Is the oil level OK?
I just put some oil in it today. The oil light came on for a couple of seconds. The clicking sound is all the time not just in the morning. It's happening whether the car is in motion of idling. Maybe it's an exhaust leak. It sounds bad and it's a new sound.