Weird Ultrasonic issue

[DiamondWash]

I thought we were having an issue with our ultrasonics because it would tell a customer to STOP then BACKUP over and over and over and it did this even when they were not under the system. So we replaced the 8-pair wires to the system no change thought we had a weak transmitter ultrasonic so we replaced it no change replace the receiver ultrasonic no change replaced the relays no change at this point I wanted semi to come through and tear the system out, we had recently painted the stainless steel plate underneath the ultrasonics yellow so I flipped it back over to the silver side checked the d timers on the ultrasonics and they were the same tested a vehicle and IT WORKED flawlessly flipped the plate back over on the yellow side tested a vehicle and it screwed up it's on the silver side now but why would the color yellow cause the ultrasonics to mess up?

 

[ibspuds]

Here's my $.02, perhaps the paint is absorbing the ultrasonic signal more than the non-painted surface??? I am a former Ultrasonic Technician and this would make sense to me. Every material has a different absorption rate...