I have an 04 Mini and it makes kinda of chattering noise only under acceleration, not when just reving engine and not while rolling down the highway. It sounds more like a stalling engine than a chatter. I am pretty sure it is not engine noise. ANYWAY i took it in to the shop today and they told me it was because the passenger side enfine mount was bad. Anybody else had anything similar?

 

Check some threads in Stock problems and issues on the upper engine mount. They do have issues.