Dodgy trigger switch or dodgy motor?

Alright gurus, someone here is bound to know!

I have a V3 P90 with an odd firing issue. When I hold the trigger down the rate of fire varies. It will speed up and slow down between 8ish rounds to 2 rounds per second, almost as if the battery is going flat, but then speed back up. Ive got a second battery and i get the same issue with that as well.

Im convinced the issue is either the trigger switch or the motor (leaning towards trigger switch) but just curious if anyone has had this before and can say with any certainty what the issue may be?