2004 Volvo S40 Shaking in Reverse

volvo
s40

#1

My car has recently been shaking/bucking, but only in reverse. It doesn’t happen every time I back up, but has been happening more and more often. The moment I put it into drive, the shaking goes away. The car has 115,000 miles on it. The check engine light came on today. I’m going to take it in to the shop on Monday, but was wondering if anyone out there might know what’s going on so that I can be prepared for what my mechanic might say.