I have developed a strange noise on start up. After the air heat light goes out, and I start up the engine, it makes a very loud rattling noise, somewhat like a spark knock in a gas engine. This lasts for a couple of seconds, and smooths out and runs fine. This is the Cat C9 400hp.
Also, on my trips this fall, on a very cold morning, it ran fine for about a mile to the interstate. When I accelerated to highway speed, I developed a terrible vibration until I got up to speed. I took it to Ring Power in Florida, but they could not get the condition or any engine codes. It does'nt do the vibrating thing on warm start-ups. I can't really tell if its the engine or the transmission.