It's probably ignition noise.
Most FM radios reject AM noise fairly well, but some really stink! If you're using tone squelch, it is not uncommon for the squelch to open, but have the audio still muted. It just depends on the radio's design. This causes the scan to stop, even though you don't hear audio.
The 2005's engine is probably a Gen III, which still uses spark plug wires, albeit fed with individual coil packs. If the milage is high (>50k or so) you might want to replace the wires and properly gapped plugs which will reduce the level a lot.
Worse case, you shield the wiring which isn't easy.