New GCM 800 - loud grinding/vibration

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Other building trade
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I've just purchased a GCM 800 SJ. It's making grinding/vibration noise which is very loud  for a few seconds on start-up, and then continues to sound rough.

I found another old thread in here where this question was asked and the replier suggested that it could be the soft start noise that the poster was hearing. They linked a very helpful YouTube video which demonstrated a healthy saw being used. I'm convinced my noise is not that. I can hear the lower tone of the soft start for a few seconds in addition to the vibration or rubbing that I'm hearing. 

I've removed the blade and spun up the saw and the noise goes away but I can still hear the soft start. I've changed the blade and get the same noise.

I can't see any evidence of rubbing on the blade and it's not obvious that it's wobbling.

If I slightly loosen the blade clamp the noise goes away, but when properly tight it comes back.

the teeth don't appear to be striking anything in the housing. No shavings or marks on the teeth.

There is a slight sweet burning plastic type smell which I assume could just be factory coating wearing in on the brushes/motor.

Is this a known phenomenon with a new saw that needs to wear in or is there something off?

Any advice very much appreciated!