As my tuner (and empeg) is currently homeless (changing car) I thought I'd hook it all up on my desk....

In my car I used to get ok'ish performance from the tuner, but like you the rds signal would turn on/off quite frequently causing the sound to temporarily drop out, despite the signal strength being full. I put this down to the aerial, and since reinstalling the stock head unit in my car, I can confirm that the aerial isn't great

...Because of the connector on the tuner module won't plug into any aerials I have indoors, I got a longish piece of electrical cable and used that as a whip antenna, with a bit of careful placing I'm able to get perfect reception on the stations that I've got preset in on the empeg, however, with this "aerial" no matter what frequncy I set, I always get full signal strengh, and unplugging the aerial causes the signal strength to disappear....

So I'm pretty much convinced now that I and what you are describing is a aerial fault of some kind....

Anyway, I was bored so I thought I'd try some things!

Adrian