2 AC vents have recently started rattling or are transmitting a rattle sound. Does this need do be checked by AC person to ensure it's not possibly a bigger problem?

There's no obvious reason why the vents would have started rattling. It started maybe 1-2 weeks ago. Both vents are on the same end of the house. AC unit is roof-mounted (as is typical in our area).

I've attempted to tighten down the screws holding them in the ceiling, no change. I've also simply applied pressure to the vent to try and stop the rattle to no effect. So it's not clear that the rattle is coming from the register itself, vs. being transmitted from somewhere upstream in the AC system. I haven't noticed the rattle elsewhere in the house, though.

I don't want to ignore it, but I also don't want to pay for someone to come out if it's a potential simple fix that I've just overlooked so far.