FIXED:

Well, I went back to the workshop today arvo and explained my problem. After worrying for a few nights the mechanic said it was an easy fix. Apparently there was a small clearance between the exhaust and the heatshield which caused the vibration. It was touching it when I decelerated. He just made more of a clearance to fix it.

This might sound newbie, but I assume the heatshield is to prevent 'heat' . Since it was sort of touching the exhaust, could it melt? And was there any damage done during the weekend?