Hi Andrew, if the noise has only started to happen following the service then I would take the car back and get them to check. It would not be the first time a mechanic has left a spanner or filter wrench on a subframe. Could even be something simple like a pipe or filter not replaced in it's clip. Better to be safe than sorry.
The noise is not always their, i drove about 30 miles last night and nothing, this morning a few miles and there is the noise again. Its coming from underneath where you rest you foot in front of the brake pedal.
It may sound stupid but if the if the noise is intermittant try having a look at the o/s front wheel if you have the old steel wheels for cracks.On my Carens Ihad a knocking noise coming from what I thought was the bottom of thesteering column.After three different garagestried and failedto detect it, I noticed the crack in the wheel and changed it and noise disappeared.