Beat knock on exhaust when I accelerate

Beat knock on exhaust. Can you explain?

Where is the smoke coming from, what color is it, have you checked the catalytic converter to make sure it isn't loose inside?

If it is blue, then oil is burning. Listen, if this is the original engine / miles, chances are the #4 cylinder is low on compression due to an issue with rings. As a result, burning oil and fouling the plug and causing a misfire and power loss. Chances are that the oil burning has damaged the catalytic converter. If the mileage is correct, I recommend checking engine compression.

Before anything is done, you should check engine compression to confirm that is the problem. As far as your mechanic, I think you are a little confused. Most likely, he said to replace piston rings and while they are out, replace connecting rod bearing and main bearing in the engine.

Checking engine compression won't stop the problem. It will determine if you need piston rings. Replacing rings and bearings is an expensive job, and I just want to know if that needs done before you spend that kind of money.