Thunderbolt Duo Fan keeps coming on, even when iMac is asleep

My TB Duo is always left on and connected to the iMac
The room has aircondition at a temperature of 26degC

Even when my iMac is asleep, the TB Duo fan can spin up and the drive becomes very loud
On a few occasions, the amber light had come on and I had to switch the drive off.

This has been happening since day 1, except now I don’t see the amber light so often.

What is the problem here?



Could be a backup software working on the background?

Have you test the unit with the drives utilities.

Thanks for the reply.

Yes, the Duo tested ok with the utility.

I do have time machine backup. I have set the backup time to every 24hr rather than every hour.
However I have excluded the DUO from time machine backup.
What I don’t understand is even if the iMac is ‘woken up’ by the backup,
why should the DUO run till a state that the fan comes on.
I would expect the DUO to run silently and then shut down shortly after.
Instead the DUO seems to run louder and louder even after the iMac goes back to sleep