Stan, Check the bearing on the pulley for the ac ( There are two pulleys with bearings, mounted close to each other). Sounds like the bearing is trying to go out. If it does while going down the road, itwill lock up and cause the ac belt to come off. Check both of these bearings, they are an over the counter part at the local pep boys. Or check with you favorite Delorean parts place. It is very easy to change. The noise may come and go but be aware if this is your problem it will go out all at once. Cost for a repalcement bearing last time I changed mine was $4.00. Also if this is your problem there is a great how to in a past issue of Delorean World. If you dont have the issue give me an email and I'll get you a copy of the section. Bruce Battles Vin 06569