peageot 206 warning light with rattling??

The warning light comes on and beeps every few minutes with the car rattling/shaking for upto a minute. The rev indicator flicks between 8 and 14 when this happens. I have had two garages look at it, one thought it was an indicator then the ECU, but wasn't sure? the second garage thought it was the coil but it wasn't and still can't find a solution.
Does anyone know waht it may be???