Problem with M1A sound cutting out
I just got an M1A from an online retailer, installed it in my guitar and find that when I strum somewhat hard the sound cuts out until I stop playing then comes back after a second or 2. I thought it might be the strapjack so tried it with a different cord and it does the same thing. I then took it out of the guitar and found that the same thing happens if I tap it hard with my finger. The pickup sounds great when I play gently and I'm hoping this isn't normal behaviour. I know there's a moving coil inside, but surely it is made to withstand some pretty strong vibrations or it wouldn't be very useful.
When the sound cuts out, it doesn't actually cut out entirely, but reduces dramatically in volume.
Any suggestions or do I just have faulty pickup? I live somewhat remotely, so I can't just take it back to the store and get a new one. If I'm doing something wrong, please let me know.