My sensors on my LS 430UL have recently started going off when I'm no where near an object.
Is there a thread related to this issue? Is this fairly common on the UL?

 

First thing you should do is clean the opaque ring of each parking sensor using a soft brush and mild soap. Often times, the ring is dirty with road debris or bug juice blocking the sensor and causing a false trigger.

 

The issue is common with all LS430's with Park Assist. The fact that the car has the UL package does not make it more prone to this issue.

 

With my high mileage '04, the paint has come off the sensors.
When the paint is peeling off in pieces, this upsets the sensors; all I do is scrape the loose paint pieces off and things settle down.
When time permits, I repaint the sensors; they work fine afterward. It's a fiddly job, but doable.
(Large insect remains can act same as peeling paint.)