Is it a 'beep' or a 'click' and is the noise directly related to engine speed?
If it is a 'click' and it is related to engine speed it sounds like HT 'pick up' but if the sound is more like a 'tone/beep' then it could be a 'logic derived' pulse, (but still related to the engine speed - such as the tacho feed - although I do not know where this is obtained from without looking at RAVE).
The obvious question will be that of 'was the noise there previously, (before you installed your microphone), and if it wasn't, (and you have now put the Head Unit back as it was previously), you could have disturbed some of the audio cables so that they are now alongside your tacho feed cable - just a thought?
Otherwise check the usual 'earths' to the Head Unit just in case you have disturbed one and lost some RF shielding.
I only have the 'standard' unit in mine and I took everything out, (when I stripped her down), and mine is still working fine with no discernible 'noise', (and I wasn't overly careful in the placement of the associated cables), but I have yet to road test her!