If it is something they did wrong like not mounting it correctly, have them also check for stress fractures as well. I have a friend who had some engine work done on his S4 only to discover when he got it back that on hard acceleration, his hood would bump up. Couldn't figure it out until he looked underneath and saw they'd forgotten to put in a couple bolts on the engine mount. He could actually climb underneath and lift up the engine. The constant vibration and bouncing on the mount ended up cracking a couple of the L-shaped mounting pieces.
Or it could be something benign like a socket wrench still stuck on a bolt or something... you know, kind of like doctors leaving a scalpel in their patient