So what is the issue? P38 fans do not turn all the way off by design. They turn down to a low speed by design to maintain air circulation in the cabin... as posted numerous times included just a few days ago.
I have similar problem. From the sound, it's just the right hand side motor on my Rangie that is doing this. I suspect the relay is blown, but the person I bought the car off said he'd replaced that. However when I had a look at the pollen filters this is what I found!
I then had to get a vacuum to suck out all the crud in the cavity where i'd pulled the filters out. The poor blower must have felt like it was trying to suck air through concrete. So new pollen filters and relay on order and we'll see if that fixes the problem. The vehicle seems really well maintained, but I read on this forum that often the pollen filters get overlooked.
Don't know if this helps you, but it's another thing to check.