I've got an 89 sc with 90k. My son has been driving it the last 3 months. I just got it back and it has a bad vibration over 20 mph when you coast or push in the clutch. It's not as bad under load. Any ideas what to look at? I'm going to check the u-joints and tighten stuff up but you guys always know about the quirks of s/c's so I wanted to ask. Thanks.