No worries. It's one of those really pain in the arse things to pin down. They only way I've done it in the past is with a very reliable mate sitting in the drivers seat with his foot on the brake while I crawl over and under the car with a bit of hose as a stethoscope.
Not it the best from an OH&S standpoint. Haven't had it happen in the disco yet, but probably because mine doesn't have a transmission. In other cars it has generally been something loose on the engine (AC compressor bracket for example) or engine or transmission mounts.

