2002 Nissan Maxima,V6,Automatic

My issue is that when my car is idling I hear a repetitive knocking sound, more concerning though is that I have a V6 automatic, but as I accelerate the car seems to be hesitating or switching gears as if it is a stick shift. This happens when I accelerate to 20mph, then again @ 40mph. The RPM go from 1 to 5 abruptly when this occurs. It feels like the engine is being muffled. Do you have any idea what may be the issue?

What year is this and how many miles?

There is more than one possibility and it needs to be looked at, but the knocking combined with the shifting problem suggests that you may have a bad engine mount.

In addition to a bad motor mount, it is very possible that the OP’s transmission is slipping.
If the RPMs “go from 1 to 5 abruptly” (actually 1,000 to 5,000 RPMs, baakchoy), that is certainly not an encouraging sign for his/her transmission.

This car needs to be taken to a well-reputed mechanic sooner, rather than later, if the OP wants to hold down the repair costs.

Thank you for the information. In response my car has over 160,000 miles and I did have the engine mount replaced approx. 3-4 months ago if that sheds further light on the potential problem. Does that change the advice given at all?

If you had only one motor mount replaced previously, there is a possibility that you need additional motor mounts replaced. The engine has…at least three mounts…and very possibly more than three. Transmission mounts are also a possibility.

Take the car to an independent mechanic in your area for a thorough examination of all mounts, but allow the mechanic to diagnose the problem himself. If you tell him to replace a part and if that fix does not work, you will still have to pay for that “fix”.