I recently bought the D130 doorbell camera.
 

Everything has been working reliably and perfectly, apart from the audio quality from the doorbell's in-built microphone, which isn't half as good as I was expecting. 
 

When using live view, or even listening to recordings written to the SD card, the audio from the microphone isn't very loud (even with the doorbell's microphone slider up at full volume in the app), and the voice of the person at the door can cut in and out if they don't speak loudly enough - just a guess, but it sounds to me as though some noise reduction processing may be going on, but that it is set too agressively. Also, if you listen carefully to the audio (both live view and recordings), there is a constant low-level background crackling/sizzling noise. 
 

The upshot is that it's difficult for me to hear what a caller is saying via my phone's speaker, especially if they stand slightly away from the door or speak quietly and if I'm not in a quiet environment when they come to the door. 
 

I'm trying to work out whether I have a faulty unit, or whether this is a limitation of the design/current firmware of this model. 
 

I'd be grateful if any other D130 owners could let me know if their audio sounds similar to mine, or if they can easily hear callers at the door (and outside ambient noise) loudly with no drop outs or crackling. I use an Apple phone. 
 

Many thanks in advance.