ATA error count increasing- Bad disk or bad chassis?

Thanks both for your help. All sensible advice.

So, on your recommendation I:-

 1. Performed a full back-up to an external USB device. Current ATA count 32 on drive 4.

 2. Downloaded the Configuration files so that I can get it back to its original state.

 3. Brought it into the house (it lives in an IT wall cabinet in an outhouse/office built 15 years ago and with power professionally installed, but, just in case the power to the building is a bit suspect, I brought it in)

 4. Re-booted in the house. ATA count went to 36 on re-boot.

 5. Powered off and power supply changed (I have another RND214 with 4x WD drives in it so used this power supply instead). On re-boot ATA error went to 40. 

 6. Powered off, pulled the 4 HDDs. All numbered as they came out.

 7. Put the 'old' HDD into slot one and  did a factory reset. No increase  in ATA error (it still reads ATA error number 49, which is what it was at when I pulled it and got the replacement)

 8. Transferred various files differing in size from 50mb to  14GB. No change in ATA error count. 

9. Between each file transfer did a restart. No increase in ATA count on any restarts.

10. Powered off, pulled the drive in slot 1 and replaced it in  slot 4. Re-boot. ATA error went to 52.  Recently moved files still present on the drive and shown as 'healthy'.

11. Two  further re-boots. Each time on boot the ATA error increased to 55 and then 58. Between re-boots transfer of large amounts of data with no increase in ATA error.

So, my conclusion is that it is a problem with slot 4 on the chassis, unless you guys can think of an alternative reason. The power supply seems OK.

 I have a couple of questions:-

    Does it matter? It looks like there are increasing ATA errors on start-up  which seem to be sorted within a 5 second timeframe on start-up and then give no further increase during the up-time of the unit. Performance is fine, and it does not look as if the disk involved is failing. The ATA errors are an increase of either 3 or 4 on each boot. If I monitor this for a sudden change, would that give me warning that the disk  may be the problem?

 The unit is still under hardware warranty, but any interaction with Netgear Support  makes me lose the will to live. I  could simply return it to the original vendor for a replacement.

 How do I re-establish my old volume and data with the other 4 drives I've pulled?

 My plan is:-

 1.Power down. Remove the drive from slot 4. 

2. Boot up with no drives.  Factory re-set the device.

3. Re-install configuration files downloaded before first factory reset. Power down.

4. Re-install the 4 drives in their correct order.

5. Re-boot.

Will this work, or is there a chance it will see the 4 drives as new and re-format them? 

I'm grateful to both for your time in helping me with this.