My beloved VX started making a 'clicking' noise about a week ago. No Isuzu dealer in town so took it to a ma and pa shop and they thought it was an exhaust leak. However, after thinking about this, I am convinced it may be 'chatter' from the front dif. So, can anybody help me diagnose this by answering the following;

1) For those who have heard dif chatter, does it sound like a metallic clicking?

2) Is the nosie worse when it is cold, and sorta goes away after it is warmed up?

3) I recently moved from balmy North Carolina to northern Wisconsin, and it is sorta colder up here, and by coincidence, I noticed the clicking sound when it started to get to 15 degrees at night.

4) I used royal purple 75W140 in North Carolina, what should I use in the colder climate? 75W90? And probably the limited slip gunk?

Thanks