What could be the cause of the increasingly worse&loud rattling noise in my car?

What is your question?

2011 Nissan Versa. Since I've owned car it has a rattle that happens more when the engine is cold. It happens in P, R and D but not when moving only idle. It has gotten gradually worse and louder. It sounds a bit like I imagine rocks in a washing machine might sound. Theres no check engine light. It runs well otherwise. 1 mechanic said it might be the casing? around catalytic converter. 1 said the tensioner is broken. I've been told too that the engine is jumping around (the guy was looking under the hood when the car idled). I've recently replaced both front cv joints, and 2 motor mounts. Front and back brakes were done about 7 months ago. 2 new rear tires. 2 alignments. Balanced all 4 tires. Doesn't use oil or transmission fluid (no leaks). I'm at a loss. I drive for Lyft but I can't with this noise. Please respond asap. I'd greatly appreciate it. Patty Derrah

What makes this problem better or worse?

It is worse when engine is cold

How long has your 2011 Nissan Versa had this problem?

More than a year but it has gotten a lot louder in recent weeks