Why are my RAID 1 Mirrors constantly "Verifying & Repairing"?

I have 3 RAID 1 Mirrors, a 1.5Tb and 2 X 2Tb. I run fully updated Windows 7 64bit on a Gigabyte P55A-UD7 motherboard. I have been running happily for a couple of years.
Recently (last 2 weeks), every time I switch my desktop on I get "Verifying & Repairing" in my Notification area. When I double click on it and run IAStorUI I see that all three of my mirrors are "Verifying & Repairing".
Few days ago one drive of one of my 2Tb mirrors died. I ran for a couple of days with the "V & R" message on 2 mirrors with the third mirror "Degraded". I replaced the dead drive and this time it rebuilt while the other 2 were "V & R"ing.
Next time I switched on - NO "V & R" message/warning so I thought "Yah! fixed it"
Next switch on - "Verifying & Repairing" warning AGAIN and since....
Anyone any clue what is going on? Can I fix/stop these warnings? Is another disc failing?
I am worried enough to consider "splitting" ALL my mirrors as it can't be good for the drives to be constantly "Verifying & Repairing". The "V & R" runs for about 6 hours
"Oh, yes", how do I split the mirrors (change the mirrors back to 2 separate duplicate(?) discs and manually sync them)?

What brand and model hard drives are in the mirrors?

The 1.5Tb mirror are 2 X ST31500341AS discs

The first 2Tb mirror are 2 X WD20EARS discs

The second 2Tb mirror WAS 2 X ST32000542AS discs but when a disc failed I replaced it with a WD20EARS disc.

I know you shouldn't mix brands but when the Seagate 2Tb failed I only had a spare Western Digital at the time.

The "V & R" process started when I installed a 4 port USB3.0 PCIe card which I have since removed but the problem persists

You're up late :)

Thanks for the response....

Yeah I need to get a life. :)

I can't say if this is the reason, but none of those drives are really designed for RAID. If fact "green" drives, because of their power characteristics, are not recommended for RAID.

It's hard to say how they get when they age and mixing different drives, as you say, is definitely iffy.

Can't think why else

I suppose I have had a good run. Just checked my original invoice, my system is 39 months old. :)

I suppose I can't just "split" my mirrors? I remember my Unix days, we used to split the mirrors everyday. We would "split" the mirrors, continue to run the system on one set and backup the other set to tape at midday.

Thanks for your response :)

You should be able to split the mirrors. With Intel controllers, just deleting the array will accomplish this.

I always back up data first but I have never had an issue.

I normally remove one of the drives then delete the array. Remove that drive, install the other one and delete the array again.