Double check the antenna wire make sure you do not have any extra coiled this can cause radio interference.
Do you have a friend with a car gas or electric take his receiver and plug in your car and see what happens.
Is the anteena on the TX removable make sure it is screwed in firmly.
Most of all make sure all wires are clear of metal, turn on the radio gear and play with each wire and takes note of any glitches.