39-194 grinding sound

I'm not sure why your are getting the grinding sound. I suggest removing the operator completely from the window and then opening and closing it manually. See if you still get that sound. Also make sure that the 39-194 is identical to your old operator. if it differs in any way, let me know. It could be that the operator arm on the new hardware does not match up to the original. Take a look at the gearing in both operators side by side.