It sounds to me like they have come loose on occasion in the past.
I had this happen to me a couple of yeas ago, and I tried to retighten the wheel nuts When I did, half of the wheel studs snapped off. I replaced all of the wheel studs in the affected hub, and hoped for the best. I ended up having to replace the rim a couple of months ago, as cracks began to appear in the rims and the holes were worn.
With this in mind, it would be best to replace the wheel bolts at the same time as the rim.
HTH