[Stu_D]

Jonathan , I'm with Rusty on this one . It looks like a loose connection with
the count going up with the vibration increasing . Its always a hassle when
all the leads are bundled together , if you pull on one who knows what other
leads have been effected . Your side aerial from the base receiver also look
to be pushed up at 90 deg not out to the side as it should be .
There have been some cases of poor performance when the transmitter
is low on voltage as well .

My installation is almost the same as yours and its 100% fine is so I would
lean more to a loose lead or plug as Rusty said .

Stu